I rarely disagree really strongly, but on numerous shows I've done, I have been allowed to play other people's guitars through their systems and I KNOW for absolute certainty that the player is key in the sound. One of my friends plays bass for a well known Soul Icon - I have played his bass and I do not sound remotely like him, not a tiny bit. I even played Rick Parfitt's Strat once pre-soundcheck and I did NOT sound like him.
The person is key, not always the instrument.
It's not even just guitars - A Hammond organ is a kind of standard, but the player is able to make them individual. I was playing walk on the wild side with a double bass in a studio - I thought it sounded pretty close to Herbie Flowers' original, when he walked in and showed me how it really worked. His fingers vs mine, on my bass, and it sounded totally different.
I therefore will continue with my opinion.