Define "far and away" for me please. Bogut and Amare are elite at defense and scoring, but Varejao and West aren't THAT much worse. Definitely wouldn't say far and away.
Eh, they're a lot worse. Amare has proven he can do what he does without Steve Nash, but David West has not managed to succeed without a very good PG feeding him the ball. On top of that, when they play each other, Amare is better than West at every facet of the offensive game, plus he gets a few blocks here or there.
West is shooting 42% against Amare. That's gotta count for something pretty significant.
Varejao meanwhile is a very useful plsyer, but he's at his best playing off of a defensive big who is the real anchor, taking on the other teams' best scoring option. You're asking him to do tsomething he's not very good at by being your anchor, and you're asking him to guard a position he's physically out-classed at, at the center.