Catch up with, yes, but hardly pass (let alone "leap-frog past").

Exaggeration aside, the point is a valid one, IMO. But people qualifying based on the promotion aren't doing so any less "legitimately" than those doing it one of the old-fashioned ways. The programme is AA's, to do with as it pleases. The "elite ranks" might well be boosted for a year, and some elite members will be more elite than they might otherwise have been, but the actual effect on existing EXPs is unlikely to be too drastic.

It's not really that different from the challenges: either a promotion pulls people in/up who will stay around, and qualify in the usual way, or they're not really (very) frequent flyers and won't be clogging the lounges or making a stack of upgrade requests.

Edit: mvoight made two of these points while I was typing, but I'll leave this here because of my third: any dilution will be minor and temporary.