Wait, what? This air unit thing is a bit screwy. You're saying bombers can destroy gunships easily? And gunships can destroy fighters? How do air and land units interact? And air and sea units, for that matter. Modern navies don't really use battleships either, it's all about aircraft carriers.
I assume the difference between light and heavy infantry is that the latter has more support weapons...
Hm. I think a more intuitive system would be something like this. I propose having three land units: infantry, support, and armour. Armour is good against infantry and bad against support, and infantry is good against support and bad against armour. That's not much of an improvement if we're only talking land units, but aircraft would be overhauled like so: gunships are good against infantry and armour and moderate against support, bombers are moderate against infantry and armour and bad against support, but neither of them has any real chance of being destroyed except against support. Fighters are good against them both and are bad against ground units and, again, cannot really be destroyed except by support. Which has a moderate chance of destroying them.
Support needs a better name. Anyway, support is good against cool mechanical stuff but can easily be destroyed by infantry, which is the cheapest unit.
...I'm not really sure whether this stuff would work out. Anyway, just a suggestion.