Sure, but heavy artillery might not survive a loss of air superiority over "friendly" territory. A deep-buried super-heavy nuke does, and forces the invaders to

Sure, but heavy artillery might not survive a loss of air superiority over "friendly" territory. A deep-buried super-heavy nuke does, and forces the invaders to slow down and try to deal with it while using other, worse routes that aren't in its blast radius, or else risk having it go off at a very inconvenient time. Like the ultimate scorched-earth plan.