it's all about what you do with what you have, and the strength of the material. Look at some of those big-voiced "divas"- aside from Aretha Franklin, none of them have been critical wonders or very acclaimed artists, mostly because the material hasn't been that strong or extraordinary.
You then have acts who may not have the big or technically fantastic voices, who are *great* artists, because the material is strong and they have an all-around appeal.
OK, voice isn't everything. A Bob Dylan will always be better than a diva that sings crappy songs. But there are also great singers that sing great songs. Take a Jeff Buckley, a Rufus Wainwright, a Scott Walker or a Sam Cooke, they are far better than Bob Dylan in my opinion.
Dumbangel I might agree with you if you list some better examples of good singers. Jeff Buckley? Artistically, yeah, I can get behind that. Singer? Give me a break. Ditto Rufus Wainright. I bought his first album but can't even listen to it because his voice is so irritating. The guy INSISTS on carrying each note for minutes at a time. Crooning is one thing, this is howling. Now if only they got Bob Dylan to sing Rufus Wainwright's songs...
"Pixies suck" - well, that's really beside the point. Thing is saying Bob Dylan, one of the most acclaimed artists in pop history, is poor because his songs don't get as much praise as his albums do or because some band is even more acclaimed is fanboyism of the worst possible pedigree. What I wrote about the Pixies was just another example of this attitude, where you're so in love with your idol that you can barely judge other artists properly.