OpenRA

or even modify base defenses in a way so that they cant attack structures at all

hm.. just an idea, cause in my opinion basepushing itself is the problem, not the structures.

what about using a cap for defensive structures?
so you can just build x pillboxes/flamestowers and y turrets/teslas inside a conyards buildrange.

you will still get an advantage of extra conyards as long ...