I love JJJ as well. Who doesn't? The problems is that to get him , the Celts would have to trade up into the top three picks. Ain't gonna happen. Say Doncic, Ayton at one and two. Then Jackson at #3. Atlanta, which is #3, has a point guard, and they have little incentive to trade Schroeder just to take Rozier (and probably take a relative loss in the trade as a result). Sacramento, at two, has a point guard. So to get JJJ you'd need to trade all the way to #1 and it would cost a ridiculous amount.
At four and five, you have two teams in Memphis and Dallas that are, again, set at point guard. So, the only realistic option to trade Rozier for a big is at #6, and you'll be lucky if Bamba is still available by then.
Is Bamba perfect? No. Would I rather have JJJ? Of course. But if we don't do this, tell me the next young big that the Celts are likely to have a shot at. Davis? forget about it. No way that happens. KAT? Minnesota will fire their coach before that happens just to make him happy. Besides, you'd have to give up the franchise to get either in the crazy scenario where they became available. So if not them, and if not Bamba, then who and when? The 2019 draft is bereft of big men, so are we waiting and hoping for the Memphis pick in 2020? These guys are rare so let's not pretend that they aren't.
Go for Bamba and if he develops a three point shot (which, according to the Ringer, he's working hard to do) you're money. If not, then we shot and missed. But to sit pat and hope that a unicorn falls into our lap is, in my estimation, foolish.