I think that statement needs to be qualified a bit-- strings do matter. Are they the sole determining factor in your game? Definitely not. But within reason, I don't think that they will jump you from 2.0-5.0 or reverse.
Poly plays like poly, multi plays like multi and gut like gut. Poly does NOT play like gut but, within reason, the original argument stands. I'm still playtesting because I enjoy it and I like helping other people. Ultimately I'm too much of a stringwh*re not to but otherwise, my hitting frames are all strung under 5.00 cost with full poly or cheap poly/synth.
"Play like to want to win, not like you want to avoid losing."