Why?

As you could read in my previous post, two positions of Dvoretsky's book took me a weekend each to adjust my ideas about chess. Now I'm working on a third position and a weekend proved to be not enough to overhaul my ideas. See diagram.























'
'
'
Dvoretsky says that if it were black to move it speaks for itself that he would trade queens since 1. ... Qf5 2. Qxf5 gxf5 is good for black.

Why?

In my ridgid vision the creation of an extra pawn island is not good. So of what comprises the advantage of black? Or is it his only way to maintain equality and are other moves worse?