OpenRA

One grenade should be enough to blow up a pillbox

Lol...I like this idea, however, I dont think it's practicle.

Well how about a separate "real mode". For example,
a rifleman should not be able to attack a building/bridge
one torpedo sinks a ship
one mig strike will level a building
an air strike leaves nothing standing
etc

Might have to adjust time to build, cost of units, etc
It would definitely make the game more strategic to have less robust units.

I would definitely love a "realism" mod!