Reduce all air unit HP and anti air damage by a significant, uniform factor. A third or a tenth or something.
To make them more vulnerable to ground units while landed, without effecting other components of air.
In a recent game a swarm of ASF were landed and overrun with mantis. They didn't take off for some time and despite this not a single ASF was destroyed. T3 v T1 units should be quite a disparity, but I feel that getting caught with your air down should be punished significantly, and is a reasonable vulnerability. At a quick glance I don't see how this would effect much else.
What are your thoughts?
A mantis can kill an ASF in a bit over a minute.