I think that OPs premise starting point isn't optimal. Attention should be on what players we need to beat CLE and GSW.
Why?
1. We can get a player, for example, of Hassan Whitesides (exp. Brook, Vuch, Monroe) stature, who are by all means good centers, and they could get played off the court versus those teams. We have been doing that at times for the past 2 years to Witeside with fine success. GSW would dissect him. They make those bigs defend in space and just torch them.
2. While I agree that we need a big, IMO we definitely need a scoring wing, two-way player more. You can classify that as frontcourt, but I see him (Exp. Hayward, PG13) more as a perimiter threat with the ability to handle the ball. You can't have enough of these players in this or any future era. Units GSW and CLE put on the floor demand 4 of those types of players.
3. You play with the hand you are dealt. Meaning, that by far the best 2 moves C's can pull of right now are drafting Fultz and signing Hayward with some roster cuts. How Danny deals with those cuts will be determined by the market, meaning if he can't get a big that can defend elite finalists units, he shouldn't force it as there are other more valuable options. We can operate under the assumption that DA will solve this issues in the top 80th percentile of GMs. Market will say, Danny will play.
4. We can always buy veteran meat (exp. Deadmon, Gibson) with the exceptions to keep us rested during the regular season. When weaker teams play traditional 2 bigs more. Also we get a prospect big in the proccess in the form of Ante Žižić.
Lets get players that we can match up with Lebrons, Durants, Klays, Kyries and Currys. That is what we need to get to the banner number 18.