I doubt that Simpson is a better runner or rusher than Milroe. The problem for Milroe is that defenses didn't really respect the passing game and were able to prevent running lanes from opening up. If Simpson can get defenses to respect the passing game, then the running lanes will be there. His running style is similar to Arch Manning's. Neither will juke anyone, but they have very good speed.I kinda doubt it.
College/pro football is QB centric. Teams don't bring in great QBs (usually judged by their passing skills) to hand the ball off or run RPO running plays.
FWIW, if TS is the starter this year I suspect there will be true balance between our passing and running. And I don't look for TS to use his legs like JM, although TS is probably a better overall rusher than JM. Just because he might not outrun JM in a straight line race doesn't mean he can't "rush" the ball well/better than JM, who was really not that good except going north and south.
And the biggest win here with bringing in Grubb to hopefully run the Penix offense we saw at UM is for the young, freshman phenom QB who's coming in this year!