I think Carmelo Anthony is actually a very good defender at both 3 and 4. Love, I am not so sure as I have not seen him enough to even know if the bad-D reputation is warranted. Rondo is supposed to be a good defender too, although my personal opinion that his defense is a bit overrated. Rondo is certainly not a bad defender.
Melo would be the big dog for sure though but I understand concerns about the mix and "coachability" of this combination. Stephens would have his hands full that is for sure. I don't think any of these potential problems would make DA shy away from this if it ever became a possibility. If there is a chance to do this, you do this, and you hope you can figure out how to make it work.