Most of the battles I don't have a problem with. In WWII, the North African theatre proved that even a modern tank division is no match for a liberal application of equal parts Ethiopian warriors--armed mostly with swords, flintlocks, and an intimate knowledge of the terrain--and kerosene. Tanks are mostly fireproof, but they get really UNPLEASANT to be in when they're covered in burning fuel.
Sure, a tank is much, much more likely to take down a tribesman, or a whole slew of tribesmen. But does that mean the opposite is not true? Absolutely not.
The gunship/knight matchups do present a bit of a problem, even for those of us with rich imaginations. Great mental images, though. "Come down here and fight, you cowardly dastard!"
For me, the best WTH moment came when I used the worldbuilder to station a few stealth fighters in enemy territory so I could keep an eye on their early development through air recon. Turns out they function pretty well without a host city...until a club-wielding barbarian comes across them. Try it. I guarantee a few chuckles from seeing the pinnacle of air superiority technology having twelve kinds of hell beaten out of it with a stout stick.