Danny Watkins had awesome college tape, and per .net's Nostradamus, he was a player our FO badly hoped would reach the 25th pick. Sometimes awesome college players are complete duds in the NFL. It happens. Watkins is old too. I'd be totally fine with kicking the tires on him next summer, but not until then (and I was a huge fan of Watkins as a prospect). Cutting McQuistan to sign Watkins would be like ditching Tjack for Matt Leinart.
I see the logic in cutting McQuistan, but I would chalk that up to a mistake move. Carpenter has less than a full season of experience at guard and isn't a lock to stay healthy. If Carp can't handle things, our next best bet is Bailey, and Bailey only played a few series at guard this preseason. Sure, Bailey was a college guard, but Tom Cable runs a very unique style of OL so those reps matter. Bowie has played a lot of guard and has looked like a natural tackle while doing it. McQuistan is a good run blocker and an adequate pass protector, and he's got excellent chemistry with Unger.
He is worth his salary, but that doesn't necessarily make him safe. Three million in cap space is a small fortune to John Schneider right now. The damage to the team from cutting Robinson was arguably more than cutting McQuistan, and he was on a $2.5 million contract. That said, if McQuistan were to be cut, I think there is a good chance we would have heard about it by now, so I'm guessing he's safe.