Here is the thing, you are assuming he will cool off and that his defense wont improve. Why cant his defense improve? Its May, he has time. Also, Lowell's defense isn't an improvement, even when Beltre is making errors he is better fielder then Lowell. Lowell has little to almost no range. Beltre gets to balls and makes errors that Lowell cant even get too. Once Beltre settles in and stops making stupid decisions one he gets to the ball, he'll be fine. Meanwhile, if we have Lowell out there, we'll need to upgrade at SS to cover up for how little range Lowell has.
Its hilarious to me how last year everybody hated Lowell defensively and an upgrade at 3B was a must, now you want Lowell back because suddenly he's a great fielder. Lol.
Edit: This is directed at themino007