Biden is way more cognizant than anybody is giving him credit for. Through prior work, I have quite a few right-voting colleagues who have met him. These are consistent Trump voters who have ALL (begrudgingly) said that he was incredibly sharp.
That's encouraging to hear. Obviously, you run in circles that the rest of us can only imagine, so I would not pretend to have any insight on how Biden "actually" is. However, I would still go with the numbers and say there is a highly nonzero chance that he can't finish a term. At his age, there's an 8% chance of dying within a year and by the end of the term it increases to a 12% chance. Similarly, even if he's fine now, his chances of developing cognitive impairment accelerate exponentially each passing year. I find it downright hubristic to run for president at age 78 (a la Trump), let alone age 82. In the 70s, we derided the USSR as a gerontocracy, and Brezhnev died at 75!