Don't think either G or Dr. D are issuing any guarantees on that :- )
What I sez is,
I wouldn't bet you anything I was afraid to lose, that Michael Saunders' UZR's wouldn't be very comparable to Guti's.
In other words, it wouldn't surprise me if Gutierrez' true value as a CF were, say, +9 runs, and Saunders', say, +5. "Comparable."
And that Safeco made either one look like +20.
............
It also wouldn't shock me if the aliens gave us the technology, and we found out that Gutierrez actually were a +15 center fielder, and wouldn't surprise me if Saunders disappointed a little in CF and was a +0, average, guy.
...................
Gutierrez has proven himself a plus -- just maybe a very plus -- CF, and Saunders hasn't proven that yet. You pencil in a 5 or 10 run dropoff with the glove, and see what happens.
....................
Saunders might very easily give you 10, or 20, more runs at the plate in 2011 than Gutierrez, if we are talking about either batting in Safeco Field.
.....................
I wish I knew why everybody in Seattle thought Gutierrez was so fast. You all have never seen him get thrown out by four steps when the SS dives in the hole and pops up to throw?