A lot of people moan that each leader isn't viable but all I seem to go up against is grunt/marine rushes, some leaders are better at this than others Jerome *cough cough* but I think to combat the rush problem without changing any units drastically is make Turrets good again, in HW1 you could have 2 turrets and hold off a leader and infantry rush, granted that infantry was weak in HW1. Also allowing turrets to be upgraded for 150 energy instead will make them even better or just make this change instead of the first.
Serina - needs a nerf but only slightly, without her freezing ability she is pretty weak.
Colony - in a good spot probably the most balanced leader IMO.
Forge - reduce Forgehog Y damage, its far too strong, I don't have a problem with his gauss damage. Scatter bomb still takes too long to start damaging but it is a lot better.
Cutter - feels more balanced, I have seen a lot more people using a variety of tactics with cutter now and not just infantry spam. I would replace Hero unit with the ODST leaders from Spearbreaker to feel more unique.
Anders - Feels perfect now her sentinels do more damage and cost 3 pop, R&D changes work brilliantly, just wish she had Hawks still. Hero unit needs a buff to bring it in line with other heroes.
Kinsano - Inferno needs to do a big more impact damage IMO, unit drops with hellcharge is still strong, would say her hero unit needs either a DPS buff or health buff.
Isabel - New hero unit or buff same as anders, Hero unit far too weak, is vulnerable early game but still strong late game.
Johnson - Colossus still needs a buff far too weak for the cost, too expensive, too slow, too much pop cost, needs stronger leader powers other than EMP Mac and Bunker drop there isn't much to use.
The Arbiter - The conduit of rage should be moved to T1 leader power to make more use of the ability, swap with teleport? Phantoms need a slight buff in HP. Other than that I think he is stong.
Decimus - The worst banished leader by far, needs a complete rework IMO his decimus drop is still far too weak, siphon doesn't do enough, just very weak leader overall.
Atriox - reduce the time Dying Breath keeps units "alive" for, reduce damage for Eradication, I would make Bulwark heal less overall as well but keep the invulnerability.
Shipmaster - my favourite leader, I would change displacement to be more expensive and have a longer cooldown as that is his main pro, but reduce the cooldown of his glassing beam to compensate,
Jerome - Omega team having inspire as well is my main problem, I am fine with them hijacking units and being essentially extra heroes but inspire should be kept for Jeromes hero only. His Enduring Salvo much like forges scatter bomb takes too long to do damage, I also find it rather weak.
UNSC changes -
Make wolverines do more damage per volley, still being outclassed by aircraft.
Would make Snipers require 100 energy as they aren't really used after an initial rush.
Hornets, reduce DPS much like banshees were Hornets are now too strong and can beat AA.
Nightingales should be tech 1 like engineers or move engineers to tech 2 to balance.
Cyclops' need to be programmed so they don't all clump together and get killed by the same canister shell, makes them useless against Tanks (which they should lose too anyway but not instantly)
Kodiaks need a damage buff, meant to be anti infantry but infantry still steamrolls them.
Banished Changes -
Require line of sight for all Teleport excluding displacement.
Make Reavers 4 pop like Wolverines and increase DPS.
Buff Wraiths not many people go Wraiths as a viable option as they are too weak.
Buff Marauders as they are too weak for their cost and cannot remember anyone using them.