Since your voice wont be heard ( by reasonable people ) on the steam forums I created an account just so I could post this here, to post what is not on point balance wise in this game
Most issues originate from the cardsystem and spacemarines being slightly underpowered but I'll start with that one problem not connected to the cards wich is that :

-The broodlord sucks .... yeah , dont even try to defend this guy . Paying a card and 3 genestealers for 1 genestealer spawnpoint that can teleport is not worth it , its simply not . He's 200% not viable because 1. he can only teleport after the deployment phase and 2. he dies like everyone else ( to a psystorm ) .He needs drastic changes to be good like either of the 2 following suggestions :
giving him improved combat stats to make him viable as a fighter
allowing him to teleport in the in the deployment phase would make him a good spawn point
either ( or both ) of these changes should be accompanied by a 1 broodlord cap in form of his card not appearing while a broodlord lives though ( if a cap doesnt exist yet, I dont know since nobody ever plays this guy )

But now to the main problem .. the card system . I think the system itself is a good idea , its a fun addition. That problem why genestealers are slightly better ( no faction is "completly broken" ) is the conversion rate of the cards.
Getting 2 action points is not as good as 3 new genestealers , not in the slightest . The strength of the active powers of the cards vary but overall they're somewhat balanced , unlike the conversion rates .
I compared genestealers "playing nomally" vs what I do , exploiting the sheer numbers you can get with cards . Normally ( one biomorph each , even the broodlord ) It actually was somewhat fair .
Then I tried getting the most numbers you humanly can with the cards,
1. bulwark 1 .reaperfex 2. miasma , always use a card that activly gets you more genestealers (gain more blips / more genestealers in a blip ), then convert one that doesnt . Repeat until the map is swimming in Tyranids and all Space marines are dead .

Funnily enough I dont think "genestealer cards are underpowered" , its more that space marine cards are underpowered .
Its more that the terminators got some of the best and some of the worst cards( like the sergants "give all action points to ..." card). Genestealer cards are usually either good to convert , got a good active or both . Terminator cards are usually good and convert well , or they suck at both.
Hope that the emperor / a hivemind will hear my prayers .

You can only bring one Broodlord to the battle. And keep in mind, Biomorph cards are NOT reshuffled into the deck. The Stealer player will only have the one.
I agree that the Broodlord should indeed be buffed. The Reaperfex is currently the strongest of the hive, by far, which is kinda silly. Originally (core rules) the Broodlord would roll three dice in close combat, and add the highest and the lowest roll together - that would be a start.

I don't think that the cardsystem is broken, or that the Marines are underpowered, at all. Except for maybe the Space Wolves.

"Getting 2 action points is not a good as 3 new genestealers." No, it's not. But on average Marine conversion will be closer to 3 AP, and genestealers will rarely draw a 3 blip.

You might be able to enhance blips and push conversion numbers in theory, versus the A.I. But try bringing your Bulwarks to the multiplayer lobby, and see what happens.

Yep, Broodlord needs a buff. Both attack and defense instead of teleport.
Miasmic also needs a buff, ability to use toxic cloud anytime, for example.

Miasma is the weaker model for sure, but it generates the highest amount of Genestealers from blips, which is important. For example:
A Broodlord does not bring any 3-blips to the table at all. And only a single 2-blip.
The Miasma brings two 3-Blips, and two 2-blips.
Miasma also gives Rubble, which is arguably the best card in the Stealer player's arsenal. But the model itself is marginal at best, it's true.

Making Toxic Cloud an ability is a good idea.

(I didnt know that biomorph cards dont reshuffle , thats good ) What you just said leads to exactly what I'm talking about , genestealers are slightly better because of better cards - and the core of that is the miasma . Experimenting in genestealer builds the final conclusion for the current state of balance is that the best combination is 3 miasma 1 reaperfex ( switched the bulwark for a miasma , its not good enough and as I said you cant have enough good cards ). Also as I mentioned , genestealer cards are better because their cards are good to convert AND to activate - the terminators cards are usually good or bad at both and here comes the not so big suprise : most of the very good cards are miasma cards . Theirs got the best conversion rate and those insane actives because lets be honest what is better than gain another blip , that blip has more genestealers and placing wreckage ? Nothing !

But I don't think the Stealers are slightly better. Sorry if it came out that way.
I get that, on average, Stealers will be much more successful, especially during these first months. But that is due to the fact, that playing Marines well, is so much harder than playing Stealers well. A single mistake, while playing Marines, will usually spell c-a-t-a-s-t-r-o-p-h-y. That is far from being the case, with the Stealers.

Changes are coming to the Broodlord. From the Steam forums:

• Removed the distance limitation for vanishing the broodlord close to an extract point.

• You can now choose any of the 4 tiles adjacent to the Broodlord when using it to spawn a blip, but can still spawn only 1 blip.