Dumble style amps are not made up for Satriani's or Vai's style of playing, so can't judge tone.  I think if Vai plugged in a Strat into JM's gear and wanted to play like Mayer, he would blow you away, that's the point.  Do you think Eddie Van Halen couldn't play tasteful SRV, Albert King, BB King blues like JM on elelctric?  EVH early idol was Clapton..he could do it better if he wanted to. The vigor that greats like Vai can play for 2 hours straight or better yet, SRV, JM could never do, he's admitted it in relation to SRV's playing, actually staing after 8-minutes, he's fingers were going to fall off.  Not bashing...love JM like the rest of us, but not a guitar God or a techincal wizard.