It would've been nice to have any depth at all on last year's team, but yes, Memo and Al would get burned horribly. Al is the purest definition of a tweener big in the NBA (way too slow to guard PFs, acceptable but unideal size for a C), and Memo has been one of the worst help defending bigs in the NBA since he was signed. From there, every problem each person has is exacerbated by the other. Al may have blocked a lot of shots, but by playing the 4, he'd have fewer opportunities to defend the rim. Since he's still faster than Memo, it would be suicide to truncate the matchups. Al's biggest problem was fundamentals, awareness, and footspeed in the PnR. As a 4, he would have even bigger troubles getting back to his man, AND he'd be put in those situations more (since there a lot more good offensive PFs than there are Cs).
Meanwhile, Memo would continue to be one to two full steps late helping anyone on D. Then comes my favorite part, where he won't concede a FG that he has no chance to stop and also won't give a hard foul; he'll slap or grab someone by their off-wrist and get them a three-point-play.
Yes. Those two together defensively would've been nothing short of a catastrophe (except against frontcourts that were almost equi-slow).