Anyone with half a brain knows the Mets, or any team, would be better with Reyes than without him.
But ...
From 2005-2008, when the Mets had winning seasons, they also had other players who were having solid years (DW, Beltran, Delgado).
In recent years when the injury bug, age, and perplexing down years have hit, of course I'd expect the Mets to have a losing record, with or without Reyes.
A better indicator would be the Mets' record 2005-2008 without him, but unfortunately that would amount to around a dozen games which is nowhere near a good sample size.