They can't do this for just Biden because whatever conditions he needs to appear normal in public are probably the exact same conditions Trump needs to do his thing.
It's not just, like, the room temperature and chair tilt, but also the camerawork and moderation that influence this, and those can absolutely be biased, though idk what the bias would even be since I'm not following this
I was pessimistic about the debate, but it was a fair deal funnier than I expected. I think Biden said something about cutting a black child in half.