In the current universe, sac 19 is worth more than lal18. It's not only expected to be a better number pick, the cap hit is delayed 1 year, and the draft odds restructuring happens next season. It's the Celtics that wouldn't agree to waiving protections. They never wanted lal18 unless it was 1 through 5.
Maybe, maybe not. Sacramento might not be terrible next year. Or Sacramento might be so terrible they end up with the #1 pick and Boston ends up with the Sixers pick which will almost certainly be in the 20's. Maybe, Boston, or some other team, actually wants a player in this draft and thus rates that player highly. Maybe Boston actually wants the salary of the rookie so it can be used in a trade (i.e. Tatum, Morris, Rookie, crap filler for Leonard). Maybe Collin Sexton, or whomever is 10th is a better prospect than Rui Hachimura, Zion Williamson, Sekou Doumbouya, Nazreon Reid, Kris Wilkes (currently projected 4-8 by nbadraft.net). I mean nbadraft.net currently has Bruno Fernando, who is eligible for this draft, at #2 next year. Outside of RJ Barrett, who Boston will never be able to acquire with the Sacto pick, the 2019 draft is pretty weak.
Sometimes the player in hand is worth a lot more than the unknown player, especially with so much uncertainty as to where that unknown player is actually drafted.