If I did not have to think about contracts, and if Kawhi is healthy and motivated, then as good as JB is (and he's really, really good) I would be willing to send Brown out for Kawhi. A five of Irving, Tatum, Hayward, Kawhi, and Horford is almost unfair to the rest of the league.
But we do have to think about contracts and we don't know if Kawhi is healthy and motivated, and under those conditions you can't do it without mortgaging the near future on a pretty big bet. The juice is not worth the squeeze.
Maybe, maybe, maybe Irving for Kawhi - swapping one big contract for another, and *if he is healthy* getting a superior two-way player. But that's still a lot of ifs and we probably end up sitting an allstar-caliber wing for part of the game(!) which is nuts.
I'd rather run it back or find some way to bring in Al's replacement.