Lebron's game won't work with a dominant center any better than Jordan's would have, or Bird's would have.
Riles created the ideal club for Lebron and now it has aged and has to be refitted.
Dominant centers and dominant 3s rarely can optimize each other.
To optimize both or three dominant players on the same team there are two historic heuristics.
Heuristic A: A dominant center needs a great power forward and a good point guard and shooting glue elsewhere.
Heuristic B: a dominant 3 needs a dominant 2, or vice versa, plus an unselfish point guard, a dominant 4 and a physical but mobile defense oriented 5.
Step outside these heuristics and you rarely optimize all your great players on a team.
Napier was not drafted to keep Lebron. Napier was drafted because Lebron is likely to leave and Riles thinks with Lebron gone it's easier to find a dominant center to go with Napier, than try build another 2/3 driven team. There is only one Lebron a generation. He is freakishly rare like Jordan.
Now, with Napier for a rainy day, Riles has to keep it from raining by signing Carmelo to keep the 2/3 axis structure that Lebron requires and use Wade off the bench.
Most any journeyman center will do. Bosh needing replacement is the fly in the ointment: not enough cash to add Melo and a great 4. So Lebron likely leaves.
If Lebron leaves, then Riles unloads Bosh too, spends a wad on a dominant center and picks up a late career power forward and is ready to go.
One thing is: Chalmers fits well off the bench in all these plans, if Mario is smart and extends his career by shortening his PT and cutting his salary, now.
Riles completely knows what he is doing.
Lebron needs his Scottie Pippen, or it won't work in Miami...or anywhere else.