Good constructive feedback - how can your issues be fixed?
If they cant, why are you here.
"Cloaking and speed are hard to deal with, but the factions seem to have mostly sane win-rates, can someone suggest how to deal with them?"
"I find I'm not able to deal with enemy firepower when I drive Necrons, what do?"
"I can never beat 'Nids, halp"
"I dont like the game-mode, and I dont like not being able to play with massive fleets in MP"
Besides the obvious "Git Gud" response -
To counter people kiting you, herd them into a corner, use your escorts to make them visible, and focus on their engines, let your automatic fire finish whatever loses engines first, and stay on target to herd them.
For Necrons, get in close, focus gunfire on one target, use your abilities to beat carrier spam, and focus a single damage type onto each enemy vessel - your win condition seems to be morale damage, so use that, break big ships out from the enemy fleet first, then bully the little ones with your guns as they try to kite you.
For 'Nids, find a way to kill the synapse vessels and you win.
If you cant cope with strike actions, dont let the enemy land them - kite, use fighters against troopships, call out where theres specific issues on this forum.
For the game mode - call out to the developers that you have an issue with it. They heard us already for skirmish, with enough talk they'll change more.
For the fleet size... well, deal, this is UE4, and some people have potato computers - I'd personally like to see some kind of "Grand Battle" 5v5 as a "fun" option once the game has been released and patched, but its not easy to do.