I think you're severely underestimating the odds of Williams being the backup 5. Historically, a freshman center ranked where Williams is (
#29 in 247's composite ranking) does not start. He often isn't even in the rotation.
As for whether Hurt or Johnson plays the 5 (i.e. guards opposing centers), I don't think I really care either way. As long as people are aware of the possibility that those two will be our starting "forwards" alongside three other perimeter players, I'm good. Once you lay out the complete roster and play around with possible lineups and rotations, 2 forwards + 3 perimeter players is how the minutes begin to make sense. Otherwise, you'll have unrealistically low minutes projections for several perimeter players. This is especially the case if Cassius returns alongside Wendell and Matthew.
Tying it back to recruiting, we don't need another center.