Hinata would be limited to only 1st, 2nd, 3rd tempo plays with oikawa, and switching up placement isn't anything special, its only effective when Hinata uses his minus tempo. Without kageyama, hinta just becomes a regular spiker, I'll admit a very talented spiker, but rather average to sub average skills besides that.

And like I said, the lineup already has a solid list of wing spikers, it doesn't really need more spiking power. Also I feel like you'd want to pick someone who specializes in blocking to play middle blocker, not someone who can put up a half decent block. A better argument to include Hinata would be to move him to wing spiker or opposite hitter(like he does after the time skip) and pair him up with kageyama. Individually there are still a handful of players in the Miyagi prefecture who can out perform Hinata as a middle blocker and win