Can we get more division between some of the races?
Imperial Navy - Adeptus Mechanicus
This is probably the most obvious one to me: The robo-boys feel like a literal reskin of the Navy. You can use identical strategies for the both, and most of their roster ends up being the same too. I'm not sure what the solution is for these two, but at this point they may as well be the same fleet. Perhaps leave the Imps as is, while the Mechs get better troops and (different) ships, but made more expensive.
Corsairs - Craftworlders
Good job with these two, they feel very different, but mostly in the sense the former is absolutely terrible while the latter is utterly fantastic. Give the Corsairs a little more love.
Protector - Merchant
As I've spammed in about 3483402395 threads by now, remove the Auxiliaries from the Protector fleet - they're good enough on their own. This would also open up a neat weakness for the main Tau faction in that they'd be all ranged. The Merchant fleet should stay mostly the same (Though perhaps remove some of the combat ships taken from the main Tau line and make them even worse at boarding), though I cannot figure out why we can't have an Auxiliary as Admiral. Right off the bat, the defensive turret ability becomes completely worthless without the option - no one is putting their Tau ships in CQC, that ability is almost exclusively useful on Demiurg and Kroot ships.
It's neat to have 12 races in the game, but only if they play like 12 distinct races.