I’ve been noticing that banshee spams have become very hard to counter even with anti air units. I had a game a while back where I had built 17 fully upgraded wolverines and sent them out to attack a large group of banshees during the late game. I began to notice that anti air units have a huge flaw when it comes to overkill. Wolverines and reavers will focus fire 1to 3 banshees per volley while the banshees are sniping down the anti air units at a much faster rate. A solution to anti air overkilling single units would be to increase the blast radius of the missiles so that a single volley can damage multiple air units.
That essentially gets down to the concept of conclaves and surface area in RTS games.
Basically when 2 big balls of units come into conflict with each other, the units that are better able to surround the other units will win.
This works because once you surround units, all of your units can fire at most of theirs, while some of their units are still pushing up into a firing position.
Essentially, if you can surround, your blob gets more shots per second than their blob.
It is notoriously hard for ground units to get a concave on air units by the nature of them being restricted by the ground they are on, or the ground they can move to in order to get into position.
This is why mixed unit comps of grounded anti air and air are stronger than pure grounded anti air.
Copy and pasted from another topic I just commented in but relevant:
This legit just happened to me in 1v1. I had all bases locked down and him cornered to two bases. but he was massing all banshees. and made a comeback! I had all wolves and he took nearly no loses. Either AA gets a buff or Banshees gets a nerf. Hornets seem fine to me thus far.