Duncan is more comparable to Bird than KG is to Bird. Duncan and Bird were the main men on multiple championship teams. You can compare KG's numbers in big games with the other two, and you can even compare fourth quarter numbers. But I've seen Bird and Duncan do a hell of a lot more in the closing minutes of playoff games than KG throughout their careers.
Confirmation Bias, you've seen more big moments because both had more opportunities.
I've also seen KG afraid to shoot at the end of games for the first 2/3 of his career.
Prove it.
Anecdotal claims of players being "afraid" don't hold much water with me.
Clearly there is no way to prove other than what you view with your own two eyes. Although there must be a reason why a much larger portion of fans have seen him afraid to shoot in big moments than have seen him come up big.
From what I can tell, it's an urban legend that nobody really wants to let go of. I use as one piece of evidence the 2008 championship run, where I spent a lot of time on message boards (both general and Celtics-based) and got to see this up close and personal. No matter how you may feel about Garnett's career, there is no argument against him coming up huge, repeatedly, in the big games/late games of the championship run of 2008. I mean, I almost hope somebody challenges me on it again so we can really go through every game if you like and I can show you just how often he was a rock in those situations.
But the problem is, even then, when Garnett came up big it was ignored and when he came up short it was magnified beyond anything I've ever seen. It's like people decided that KG isn't clutch, and then proceeded to ignore anything that didn't confirm that view...even if that meant ignoring almost everything that happened for an entire postseason.
The peak of ridiculousness came on the Sons of Sam Horn board, where they had a running thread called "Is Kevin Garnett a Phony" where they proceeded to rake him over the coals for the entirety of the run. The climax came in Game 5 of the Pistons series, where one poster adamantly insisted that Garnett shrunk late in that game despite KG leading all scorers with 33 points, leading all Celtics with 10 4th quarter points, and hit the 2 game-clinching free throws with 2 seconds left in regulation. That was the point that clinched it for me: for some, no matter what Garnett does or the bodies of evidence to the contrary, KG will just always be considered unclutch.
But in the face of all this I think it's even more clear that uninformed public opinion doesn't make something true, even if a lot of other un-informed people believe it.