What is that leverage? That they'll hold onto AD until the deadline and get even less for him? Or are you talking the Celtics facade?
The leverage is in 3 areas, imo.
1. Ainge is apparently undeterred by what Rich Paul said. If he truly is undeterred, he may be willing to include Tatum, which would make the Celtics offer tough to beat. Without Tatum, the Lakers have the better offer. With Tatum, it's damn near a coin flip and would be determined by whether Griffin likes Tatum or Ingram better. Based on their health so far, Griffin may decide he likes Tatum better.
2. The Lakers HAVE to get something done. The season fell apart on them last year and the FO has, at best, looked inexperienced and at worst, incompetent. Because of that, no top tier FA's seem to be interested in being Lakers. If they manage to pull off the trade, the roster looks more appealing to FA's and the Lakers FO looks a lot more like they might have some idea as to what the hell they're doing.
3. The longer this drags out, the more teams other than the Lakers will be emboldened to throw their hat into the ring, even if they know for certain that it's only a 1 year rental.