I still wouldn't change a thing about the OHMSS we have. So many factors make me uninterested in speculating how it would have turned out with another actor. Connery was Bond as the ultimate sexist, misogynist dinosaur (to borrow another actor's label) and didn't fit the part of romantic Bond. I suppose he could have, but it doesn't seem to be his thing, so why would he have tried even more by that point?
Romance also wasn't Dalton's strong suit, so I'm not sure it wouldn't have in 1969 anymore than in 1987 or 1989. Both Connery and Dalton had strengths for things other than what OHMSS required. Lazenby gave us a fresh look, somebody who wasn't too associated with any one aspect of the role that we couldn't accept his falling for his true love.
Also, Dalton wouldn't have necessarily been right in the 1970s when the lighter side of Bond was emphasized. Now I would unquestionably have liked him to start in 1981 or continue after 1989.
In response to Krynoid Man's claim of OHMSS having "failed" at the box office because of poor marketing, I disagree. First, the film didn't fail at the box office at all. It made money. That's an old myth based on not achieving the box office heights of its predecessors. Depends on your description of failure and if it's profitable then it's not a failure.
Secondly, the marketing was there. It was treated as an event movie just as the others had been while not getting near the marketing push TB and YOLT had. It also wasn't underserved the way LTK was. Add to that the challenge the marketing team had to deal with the fact Lazenby wasn't coming back as Bond. And that the peak of spymania had already passed. It's not like they just threw it out there to sink or swim. The effort was clearly there.