It appears you are relying on some sloppy logic Chris.
The "growing doubt surrounding Biden's mental faculties" is something that was reflected in the Rasmussen Poll I cited. You then assert your own subjective interpretation of events, which itself is false.
Biden doesn't simply stutter, he's said many things of concern during his candidacy:
Joe 30330, his comments about leg hairs and roaches, mistaking Iowa for Ohio and then talking to a wall, mistaking his wife for his sister, telling parents to leave the "record player" on...his comments about not being black if you don't vote for him/that blacks are monolithic in thought unlike hispanics etc.
None of these are the result of a stutter, they are the result of ageing and being unable to maintain a line of thought. Though again, all of this is relatively subjective. If you are ardently anti-Trump, you'll attempt to see these things in a positive light somehow.
Though we can already see with the angling of the Biden campaign and the MSM, they are priming voters that Kamala will replace Joe. Even you yourself said that "I worry that Ms. Harris is unprepared assuming Biden is incapacitated."
Why would you worry about this if Biden has no cognitive issues? We don't see similar discussions taking place around Trump and Pence.
Additionally, why am I illogical in saying Kamala is poised to become the unelected president?
She lost in the primaries handily, and although some people may be happy voting for Biden with Kamala as VP, is everyone aware that she may well take over Biden's role in the next four years? I would posit that many people are unaware of this fact.