What Gene said about hiring Ace (heavily paraphrased):
Auditioned tons of guitarists. Guys who were technically proficient, guys who could play thousands of notes. But that's like a bunch of angry bees. Maybe that's what some people like, but it's not who we wanted to be. We were looking for a sound that fit, a style that made sense with what we were doing. As soon as Ace plugged in and hit the first notes, we knew he was the guy.
Ace isn't angry bees. He fits. And he's pretty good. His guitar smokes and shoots fireworks. The first to do that kind of stuff. Do I care if he can't skibbeldy-bee-boop all over the place? Nope. I don't care for that.
Same with singing. I'm not impressed if you can hit 18 notes (Christina Aguilera, I'm talking to you) when one will suffice. I want to hear the song, not your self-indulgent wailing.
John Mayer is a bleeding homo.
Yeah you're talking about fitting someone in a band here, that's different. Doesn't make him a great guitarist. Les Claypool (Primus) was turned down by Metallica because he def didn't fit in. Doesn't mean he sucks as a bassist (maybe as a lyricists or vocalist). You need a guy that has some of the Ace flash with some of the Stevie Ray chops.
But the Taylor guitar guy, that's a totally different breed. Go look at Tommy Emmanuel or Andy McKee on Youtube. Heck, go watch Chet Atkins. You'll be impressed, but you'll be bored to tears pretty soon.
And the greatest guitarist in the world is Doc Watson.