Tom Baker may indeed have spent too long in the role of The Doctor, BUT...
...while he did indeed look a bit different by the time of "Logopolis" (with or without his change of costume, or different personality), at least he did not look too old for the role, at the end - UNLIKE Roger Moore in his seventh and final James Bond outing "A View To A Kill".
The contrast between Moore in "Live And Let Die" (where he looked younger than Sean Connery, despite being 3 years older) and Moore in "A View To A Kill" is notable, facially - as well as in relation to the ages of the women he was sleeping with!
While Tom Baker ideally should have quit "Doctor Who" at least one season earlier, Roger Moore should have quit the role of 007 not just one film earlier, but two films, or even three films.
(Had Timothy Dalton replaced Moore sooner, starting in "For Your Eyes Only", he would have had a whole decade (the '80s) to himself, and perhaps be as popular as both his successors - if not Connery, as well.)