Not a Lakers (obviously) but I don't think that's a great deal for either team though it's not illogical. From SA's perspective they get a starting forward of the future and another asset, albeit not a particularly valuable one. From LA's standpoint, they accelerate their process.

The problems are though that from SA's standpoint they don't just need to replace one player, they need to change the direction of their whole organization. Their roster is old as shit and they need at least two solid pieces to go forward with and they could probably stand to tidy up their books a little, too. Ideally they would get three pieces--a firm one and two with good enough potential that one would work out--and maybe some peripheral benefit (e.g. dumping a contract), but that may be getting greedy.

From the Lakers' standpoint they deal the guy who might be the most talented player and the closest to breaking out in their young group. That'd be fine if they were trading for LeBron or Giannis, but Leonard, though a similar caliber player, has some question marks surrounding him. One year left on his deal, just had a serious injury, just had a falling out with his previous organization, etc. Not the kind of sure bet you'd be hoping for.

Personally I would not be that attached to Kuzma if the Spurs want him (and I'd move Ball before BI) and while they have been burned overpaying in futures before, LeBron's presence pretty well ensures picking in the bottom third of the draft for a while.

It all depends on the competing offers, too, of course. One thing I find interesting is that since Leonard has become the biggest fish by far in this market, there have been some guys talking trade or departure suddenly (Butler, Lillard) and obviously the guys up for new deals next year are always at least a remote possibility. That could be hurting his value, especially with the Lakers, Sixers, Mavs, Clippers and Knicks all well-positioned for next year, among others. LA, Philly and I guess Dallas *could* make a big move now, but they don't have to.