When Cliff Lee was pitching extremely poorly in 2007, he was sent to the minors, fixed his problem and re-found his form. Other big pitching names have been known to alter their mechanics in the minor leagues, only to return with better and sharper stuff. The Yankees did it with Chien Ming Wrong this year after he got off to a slow start (and no, it wasn't because of Whiffle Ball Park).
So why not do the same with Oliver Perez? Why not send him down to the minors? By sending him to the bullpen, the Mets are going to face a bigger problem: What game are you going to send him into?
Are you going to send him into a close game in the 8th inning with 2 on and nobody out? No, it's too risky.
Are you going to send him into a lopsided game when the Mets are down 7 runs? What will we be able to take from that?
And if in fact he does come into a close game and pitches 6 strikes and strikes out 2 - does that mean he's ready to go? Negative. Getting 2 outs in a big relief spot doesn't define a pitcher's readiness as a starting pitcher.
If one word had to sum this thought up, it would be perplexing. I just can't figure it out. But hey, I'm not the one who has to pay the most expensive left-handed reliever in baseball. They do.