Lets be real, Biden is showing signs of decline as well, I mean the man is in his 80s. I'd be surprised if he wasn't. I think he's doing better just by virtue of living an overall healthier lifestyle than trump.
But the biggest difference is that biden doesn't have to double down on every ridiculous, nonsensical, half thought that tumbles, unbidden, from his mouth because the only brain cells left are directly associated with self-aggrandizement and sexual assault.