Gunships are clearly in better position than they were few patches ago.
Locusts are bit low DPS for their cost, but they make effective raiders if enemy doesn't have tools to respond to fast Locust + Gnat assault. Could potentially still use some tweaks on direction or another.
Gnats are still super good with their stun, making them exellent supports, though for similar results Widow is often better due to its stealth and long stun duration even if it was wiped the second after. Gnats still compete with their response speed.
Harpies can be used as army supports to let slower ground units catch faster enemies by slowing them down. Their accuracy also makes them good at countering small numbers of raiders as long as they manage to land a hit.
Nimbuses are effective brawlers that can melt anything with enough numbers as long as they aren't countered.
Revenants are effective at hunting high priority enemy targets. For their cost they aren't tootanky compared to Ravens if we also take into account their slower speed, but they achieve similar results and the fact that they can reload anywhere makes them really effective if got into enemy back lines and enemy doesn't have air superiority to counter.
Hercules and Charon have their uses for Snitch drops and occasional rushes such as scallop drops. Hercules is also very good at countering Crabs by simply picking them up.
Trident is of course effective AA against Ravens and Swifts.
Blastwings are probably the only GS unit that doesn't have any use proper use besides scouting. It was already questionable before when it managed to work as early raider by killing mexes, but the increased mex health took that away as well. Now it is just unit that can't really aproach any form of defence.
Air on the other hand is more of a specialised assault and support factory. The fast speed makes air units able to react and take advantage from different chances all around the battlefield from killing enemy raiders to bombing strategic targets such as Tremors or just maintaining air superiority to ensure enemy doesn't get to take advantage from holes in AA defences. Especially thunderbird is strong force multiplier in terms of stopping entire enemy assaults or rendering enemy defences vulnerable for assaults.
GS and air are both factories that will eventually get shut down by AA as game goes on, and that is fine. The existence of GS or air will force enemy to spend metal on AA which is metal taken away from ground units. The mobile nature of air units also forces enemy to cover their entire frontline with AA because otherwise you can still harass the unprotected flanks.