Its an old theory - which was pretty well supported when the situation was two actors with third films - Sean GF, Rog TSWLM - who were well-appreciated as Bond and two who dropped out early and were disregarded, given additional credence by Tim having dropped out after two so the theory goes that with a lighter touch in, say, The Property of a Lady, and with audiences more used to and accepting him in the role, hsi third might also have been his best.
Sadly, TWINE torpedoed the idea, and showed it up for what it was: a nice idea but unsubstantiated with sufficient evidence, from distant Bond days.
Agreed David. I would also say a lot of people especially on this site do not believe GF is Sean best film.
As for the proposed Dalton 3rd film, going by the script i think it would have given TLD a good run for its money as far as best film. The car chase would have been a highlight as well as the PTS of a nuclear/chemical weapons facility blowing up following robotic failure.