They are when the force is coming from someone equally or more superhuman. It's all relative, Law might have superhuman durability, but the force is from something superhuman, so it still works the same way. He was running as if nothing happened for the same reason that the pain and wincing goes away when you take your thumb off of the bruise, the force is gone. He is no longer feeling the constant push of the force on his wounds, so the pain has subsided to a more bearable level.It was just small bruises. From a certain level of superhuman strength, small bruises aren't enough to decrease your physical capacity. After Law escaped from the gravity, he was still running as if nothing happened, outspeeding even Doflamingo at times, stopped overheat, fought Doflamingo and so on, so no, small bruises on the body is no excuse and just an attempt to grasp at straws if anything.
Besides, if small bruises are enough to decrease his strength then it shows even more that he is inferior physically to Zoro when you realise the number of times even close to death Zoro(so let alone small bruises) showed to endured pain to fight as well as if he was healthy on multiple occasions
Crying out due to pain is something Zoro has always done, regardless of how strong he is, so no, it does not. Law's strength wasn't decreased because there was pain on his bruises because, as you yourself said, he was running just fine once the force was gone. I never said Law's strength was decreased because of the pain, I'm saying Law's reaction to the pain was greater than Zoro's because the force would hurt him more due to exposed wounds, while Zoro had no exposed wounds. You have either contradicted yourself, or didn't understand what I was saying.
However, what I've realized after typing this is that Law never actually cried out while under the force of Fujitora's gravity, in the manga, he is just pinned, but isn't wincing or crying out or anything. So all in all, you're still wrong about it meaning Zoro>Law>Sanji in physical strength.