RWill is improving, great to see, but we still need a different kind of big. It is nice to have him for rotation flexibility to add to Theis and Kantor but nearly all the top teams have the ability to play 2 bigs at the same time as their core rotation unit. These are all the front court pairs for the top 5-man groups, by far, for these top teams:
Bucks Giannis/Lopez
Lakers Davis/McGee, Kuzma/Howard
Clipps Morris/Zubac, George/Zubac
Raps Siakam/Gasol, Siakam/Ibaka
Nuggets Milsap/Jokic, Grant/Jokic
Thunder Gallinari/Adams, Gallinari/Noel
Celtics Hayward/Theis, Tatum/Theis
The other big exception is the Rockets. What all of these top teams have is the ability to put out two bigs because one of them is skilled enough to be a big but still provide some level of offense. Some of the bigs are more swings like say Paul George but these top team have a traditional big man 1-2 punch. Paul George is still more size than Gordon Hayward. And he plays next to Zubac, not Theis who is barely a big himself.
We don't have a big who can provide that type of offense so we can't play two bigs. So we play one big and fill in with wings. Not the end of the world, we are still a good team because we have enough talent outside the bigs to make up for it but it is still a weakness. Many people try to preach that the league has changed, you don't need bigs but it is still pretty consistent that nearly all the top teams are top teams with size. More importantly, skilled size.