Just thinking out loud here:
I agree with both sides of this arguement. As a lead guitar player who relies on FEEL for just about everything, Ed's opinion makes sense to me. You know, we've all heard the saying, "shit in shit out." If you have a shitty player through a plexi his tone is probably going to suck because he doesnt have "the touch." At the same time, one would argue, "but the core tone is still there!" And Id have to agree.
Its sort of a catch 22. I propose that tone is in both the fingers, the amp, the guitar, the strings, the cable etc etc. The variables are endless. Id say the amp and fingers are the two biggest variables though.
Imagine how much different I would sound through Ralph's Mark IV using his settings than he does! Probably quite a bit different, especially from lead line stand point! Where it becomes harder to tell, is the rhythm playing. You can still tell a difference, but now that you're playing chords so you're hearing the amps full tonal spectrum (i.e. where the mid emphasis is, low end tightness, bright/dark top end etc etc) and it becomes (IMO anyways), a lot harder to tell who is who. You'd still be able to tell the difference between Ralph and I playing rhythm though, because Im such a heavy handed player. But I dont think its as easy as hearing the leads.
Thats one of the reasons I wanted Ed to make rhythm clips comparing his SV and another tube amp. Because when he plays lead lines, all I hear is Ed and Ed's tone. It doesnt matter what amp it is. Ed is like SRV to me in the sense that, I dont need vocals bass or drums to figure out who it is, I just listen to his playing. So if all I hear is Ed's leads, comparing the two amps doesnt even matter to me at that point, because they both sound the same.