I totally disagree with this pov. Marcus is a key player and one I would love to have but I don't believe him to be indispensable. Offensively, he is limited and he will command a large contract following his rookie scale contract.
If you're going after both Fultz and Tatum, then you should move on from IT and Horford and just go all in on the young rebuild.
Tatum and Brown will play the same position. I don't think Tatum is big enough to play PF next to Horford. And I like Brown more than Tatum. And WCS had a nice end of the season, but I don't know if he really fits, at least on the offensive end in CBS's style of play.
Plus Smart is the closest thing we have to a KG type in getting guys going. IT doesn't do it, Horford doesn't do it. You needs guys like that, and they are rare.
It would be better to move pieces like AB or Crowder, Young, Yabu,Zizic other picks, for Dieng and thier pick. Mini needs some defensive vets for Tibs coaching style. Pick up Luri Markkanen who would be a better fit in Stevens style. Dieng would start until MArkkanen is ready and would be a great back up big with a cap friendly contract.
Then you could have cap after some more moves for Hayward. And in years you could have a core of Smart/Fultz/Brown/Markkanen to take over. And what ever the 2018 gets ya.
Now I would move Smart, but it would have to be for a legit guy. Tatum and WCS are not legit, not yet, so you're making a move crossing your fingers hoping it pans out in 3 to 4 years.