The Celtics need to be looking for the next Harden, ie the next max-level player whose value is way above his contract. All of the other details are inadequate in terms of vaulting them into contention. They’re just not close as currently constituted. Players like Siakem or Valanciunas don’t move the needle, at least not enough to make this team a contender.
Issue is that the next two names that seem likely to fall into that category are Beal and Towns.
Neither of those guys is helping you win games on defense. If you could get either one without giving up Jaylen, you could have a very dangerous offensive team. But is that feasible? The Celts don't really have any blue chip assets anymore other than their main two guys. So the only way I see the Celts being able to trade for a big name is if the big name guy specifically wants to go to the Celtics.
Maybe that's possible with Beal, but it seems a stretch to me that any All-Star looking for a better situation is going to put Boston at the top of his list.
I don't think they could get Towns without Brown, but I do think they'd have a shot at Beal doing a Harden type trade i.e. Walker plus 4 1st's and 3 swaps, or something like that. If they can find a team to take Walker for expirings and another 1st, maybe Boston doesn't need to include as many. Maybe you get Bertans as well saving them more money (I don't know what they think of Davis long term).
So do the trade right before the draft and finalize after (allowing the trade of back to back 1st's)
Boston - Beal, Bertans
Washington - Walker, Langford, 21 1st, 22 1st, 24 1st, 26 1st, swaps in 23, 25, and 27
Maybe you get some protection on some of the picks (like top 4 or something)
So post-trade (15 man roster)
Starters - Beal, Brown, Tatum, Bertans, R. Williams
Rotation - Pritchard, Smart, Fournier, Nesmith, Parker, Thompson
Deep Bench - Ojeleye, Kornet, G. Williams, Edwards
Obviously a bunch of different lineup configurations. Maybe you have Smart starting with Bertans on the bench. Or maybe Pritchard is ready to start. Maybe you go a bit smaller and Fournier start instead of Bertans.
I don't know if that team is quite to the level of Brooklyn next year, but it is certainly a heck of a lot closer and would certainly have a reasonable shot at beating them or any team in a playoff series.