After having played a bit of Tyranids, and confirming that this is indeed the case, it appears that ONLY the Tyranid hiveship counts as synaptic control for the purposes of morale.
While this has lead to some amusing situations, such as a second or even third hiveship losing its morale and fleeing the battlefield, I think it's pretty obvious as to why this is a bit of an issue in both a gameplay and lore sense.

Firstly, lore-wise, Tyranid fleets aren't really supposed to have a singular leading synapse ship. Yes, hiveships are very important and killing them will disrupt the fleet, but there's going to be a lot of hiveships. Their entire point is that each hiveship is the strongest link to the gestalt hivemind there is, forming a distributed command of the entire fleet.

Gameplay wise, this makes Tyranids exceedingly vulnerable to admiral sniping, considering their absurdly low bravery, as well as the fact that their hiveships are rather fragile compared to most other BS', as well as being fairly slow and ponderous (barring the Rush ability) overall! Killing the Admiral hiveship early on may as well be a GG as soon as it happens, since it's all but assured that the entirety (or 90%) of the remaining hivefleet is going to instantly mutiny and run away.

Personally, I'd expect for there to be some benefit to taking multiple hiveships for redundancy, or even BC's with their fleet synapse upgrade. There are a few ways I see this could be done, and I'm curious as to what the forum as a whole thinks:

1. Every synapse ship provides global synapse control, and every synapse ship must be destroyed in order to cause Tyranid ships to flee.

2. Every synapse ship provides global synapse control, and every synapse ship lost out of the original synapse amount causes a penalty to some kind of the fleet, with the final synapse ship lost causing mutiny.

3. Tyranid ships naturally regenerate absurd amounts of morale, but the rate of this is dependent on the proportion of synapse ships currently alive globally, with every synapse ship being destroyed resulting in a 0% rate of regain, and thus inevitable mutiny considering their low bravery.

4. Tyranid synapse ships provide absolute control as the admiral ship currently does, but only in some finite radius. Tyranid ships quickly lose morale when outside of this radius. Perhaps have this radius be larger for the admiral hiveship, and also upgraded by the BC synapse upgrade? As an example with random numbers pulled entirely from the ether:
   Normally, hiveships have 13.5kkm synapse, and the admiral ship gets +4.5kkm synapse range
   Upgraded, devourer's have 9kkm synapse, hiveships have 18kkm synapse, and the admiral ship gets +4.5kkm synapse range

I'm sure there are many other solutions, but those 4 are the ones that stuck out to me most immediately.
Personally, I'm partial to the 4th option, along with a significant decrease in price to Tyranid escorts to really drive that "massive swarms of droneships clouding around massive hiveships" idea from fluff home.

What does the forum think of the problem as presented overall, and the solutions proposed?

I was very surprised that only the main Hive ship provided synapse. This should be changed to every hive ship, to mirror the TT. Sniping synapse was a thing then and yes it will be a thing now which is why I always ran 2 Hive ships as soon as I could afford it without over stretching my fleet.

Alternatively an option where your ships don't flee could possibly work. In the TT game there was a chart you would have to consult to see what your nid ships did if you did not have synaptic control of them. This could easily translate to you losing control of the ship and it engages the nearest enemy ship. This would promote the "disruption" of the Hive fleet we always hear about without having your fleet breaking shortly after your flagship is slain.

While I'm ranting about tyranids I'll give my 10 cents on them as a whole. Their not bad, I'm fine with them being alittle squishy because they were in the TT game, they just need some offensive help.

Pyro acid batteries, as they stand I don't bother with them. With troop damage and direct hull damage taking the spot light with nids I just don't see why I would invest in giving my opponets the usefulness of their shields. Maybe I'm wrong, just how I see it.

Ramming, one of the primary ways tyranids get alot of damage done. Brace for impact is great for this but not always available. A small racial mod would be helpful even if it was load out dependant.

Massive claws, this is more of a wish list item. In the TT when you used them if you made 2 4+ rolls the tyranid ship would attach itself to the enemy vessel and continue to attack every turn with its claws until it was dead or opted to leave. If this could be realized, one it would be amazing to see but I think it would breath more life into the lighter tyranid craft. Does with massive claws were very threatening back then.

Drones, as a while im very disappointed, I find they are far to expensive what what they bring. I have found only 2 ways to use them. Either bringing 1 or 2 of them and try to cap the enemies backfield mid to late game. Or comprise your fleet of as many as possible. One possible way to buff them is to let them board. Escorts only rolled 1 die in the TT game on average because they would only have 1 structure point of health. However since tyranids doubled their boarding rating tyranid escouts could be threatening when in came to boarding. 4 tyranid escorts rolled just as much dice as most other factions vanilla grand crusiers.

I could keep going but I'll stop for now.

@lordprinceps Pretty sure it doesn't need to be a hiveship. Whatever the admiral is functions as the synapse node.

already explained it in discord
but few wrong assumptions that i should probably repost corrections to here

1.you dont need a hive ship
you just have the admiral ship and thats the ship that holds your norn queen that is the core of the synapse of the fleet
if you just want to have reliable synapse you can have a admiral LC and hide it in a corner
hive ships are just good as synapse because its the tankiest ship you can put it in

2.there is an upgrade that gives synapse to all BC and BS in your fleet
my all jaw devourer fleet had that as every ship had jaws so every ship needed to be disposable
sadly it kindof became an autopick as its not really as sacrifice to pick it over the others as like mentioned above pyro macros (and all ranged weapons really) arnt worth caring about

a problem is that hive ships where too good making people build a hive ship fleet
meanwhile other nid ships where just horrible and ridiculously overpriced so no hive ships where ever used as a tanky place to put your norn queen in safely while you swarmed your enemy in pyro LCs buffed with instinctive targeting
a fleet like that simply didnt work because nid escorts where some of the most expensive and that overpricing continued all the way up to devourer so there where barely any hive fleets that felt like a swarm at all
you got hive ship only fleets everywhere, tho why so few people used the synapse link upgrade i dont know

also

• Upon the extinction of the class of xeno-form known as a Norn Queen, a psycho-temporal event approaching level Gamma 12 is generated – a level sufficient to temporarily obscure the light of the Astronomican. It is believed that this phenomenon represents the 'death knell' of said xeno-form, and that its purpose is to trigger those bio-vessels that intercept the signal to calve. This has been dubbed the 'Hydra effect', for, upon the death of one Norn Queen, a number of others are calved and thus the advance of the Tyranids is merely slowed, not stalled.

ofcourse lore on norn queens is rare as they are in a hive ship and people rarely go into those
but from that effect it sounds as if there is one center focal point of the hive mind (admiral ship) else losing one wouldnt cause that panic in the hive to breed a new one in a lot of ships

@solaire

You are correct, which helps simulate a splinter fleet. I'm just saying it should be a passive of every hive ship, not being flagship dependant for that specific unit.

Screw lore or whatnot.

Yes, I feel that hive-ships should at least have a local AoE morale buff, even if they don't have the absolute morale advantage of your flagship.

Right now smaller ships are quite bad for nids, in real part because if your flagship goes down they insta-run. They wouldn't be great anyway, but there really should be some backup here.

Fleet differentiation is already a bit weak, supporting local morale effects for larger ships (and weaker larger ships) is a great sort of combo to keep things interesting.

You cant just say screw the lore, its the foundation for the play-styles and composition of each fleet. Im not saying its a unbending law that must be strictly adhered to, but it should at the very very least be a guideline. Its the source of your flavor, Im going back to the table top for a prime example of lore impacting fleet composition. With the Imperial navy I needed X amount of escorts to unlock 1 capital ship, with Tyranids I needed 1 hive ship to unlock X cruisers and X escorts. Why does did this matter? It had a direct impact on the number of each class of ship in the respective fleets directly impacting the tactics used by the player. Im not saying devs need to do something exactly like this, but to disregard each races lore will result in a fouling of their respective compositions and play-styles.

@Ashardalon I didn't realise the BC upgrade affected hivehips too

it says BC and bigger
hive ships are bigger
its an almost essential upgrade honestly, probably too strong
it makes pure hiveship fleets close to impossible to stop once they can get close
honestly prefer nids as having one focal point, its both more fun to play and to counter
sadly with the low numbers its not very viable

Well I never lost to an admiral snipe but I came close, I definitely would have taken it over my choice if I realised that was the case.

its how i won all my nid vs nid fights
usually first thing i go for and check when fighting nids as another faction
especially if i dont see escape as reliable
only way i won vs echo using your fleet build when my entire fleet got the boost bug