Here are some I have mentioned before:
- Hulk shouldn't hit that hard. f=ma or p=mv, whichever you prefer. Either way, speed is an important component. Hulk is heavy but doesn't have superspeed. He has the strength to ensure that all of his bodyweight is behind a punch but if he weighs 1000lbs, he should only be hitting 5-7 times harder than a decent boxer. Spider-man should punch harder than Hulk. Now if it comes to grappling, no chance. Hulk will squish anyone.
- Spider-man should be bullet proof, at least from small arms. He can lift 10 tons, making him more than 100 times stronger than an average man. If he can lift 100 times more, his bones, tendons and skin etc also need to be proportionally stronger. So a bullet would feel 100 times weaker to him. A .45 would feel 10 times weaker than an air pistol to him.
- A common explanation for Superman's ability to fly is that he manipulates gravitons. How does that help him move in space? Or move left and right? He would need something heavy to attract or repel against.