I'd like Monroe or big AL but that brings up questions on Sully IMO. As others have said in the paint bigs are not the same need in today's game. One major low post scorer is all you want in your big man rotation. Need more defenders and spread the floor guys. PnR and stretch are what works right now. Only exception is space eaters with big size and length like a Drummond, Gasol, Gobert, Jordan and to some degree Duncan. (Hibbert could be space eater but he disappears) So basically if Cs sign Monroe or AL, Sully would likely be traded. And Monroe and AL may not fit the philosophy of today's big man roles. Yet they are very good low post bigs, decent rebounders and man defenders at the 5 even Sully is ok. At the 4 they get shredded on D but can score easily. A lot comes down to strategy.
Drummond and Monroe doesn't really work as Pistons record shows so I feel Monroe is better at the 5 with an athletic 4 that can at least shoot from 17'. Bass, Ibaka are good PFs that fit. Porzingis, Portis, and Harrell may be draft options that fit.
Still you have a low post big already in Sully so is it wise to invest $ in another low post big that has many of the same flaws? WCS if available would be great with (under 250lb) Sully. Porzingis, or Portis would also look good with (over 255lb) Sully.