The thing about Lazenby is, he never got the chance to grow into the role and become more at ease in it. Connery was excellent from day one, but he really hits his stride in Goldfinger, his third outing. Moore's best performance is in TSWLM, also his third.
For a former model, Lazenby acquits himself pretty well in his first movie, especially allowing for his being dubbed for much of it. But imagine if he'd gotten to return to the part. Particularly if he'd been cast in a Diamonds Are Forever which was more in keeping with OHMSS instead of the campy outing we did get (probably as a result of negative response to OHMSS, admittedly).
People have speculated that 007's grim hunt for Blofeld at the start of that movie is that he's out to avenge Tracy but that's undermined by a different actor as Bond, different actor as Blofeld and very different portrayals of each character. Now, had it been Lazenby hunting down Savalas ... Oh, the potential.
Lazenby was born in 1939 (as oppose to Moore's 1927 and Connery's 1930) and could quite easily and convincingly have played Bond well into the 1980s (eg Brosnan was 42 in Goldeneye and 49 in DAD, Dalton 43 in TLD). Just such a waste, really.