Russell is just a bad fit for Mullen's offense. For everyone that keeps saying he is going to tailor the offense to fit the personnel, they are just lying to themselves. Mullen has an offense. He is going to run that offense. Sure, there are some wrinkles that fit Russell fine, but overall the offense is not a great fit for Russell.
Now Russell isn't immobile, but he also isn't a punishing runner. Mullen runs the ball with his QB. Hell Tyson Lee ran it 74 times in 2009, and he weighed about 180 lbs soaking wet. Regardless, Mullen ran his offense which requires the QB to run the football.
Look, I don't think Coach is saying Russell is a bad QB, he isn't. I don't think Coach is saying Russell won't have plays that he can perform well in Mullen's offense, I think what he is saying is that Mullen is going to run the ball with the QB at least 150 times a season. That is a bare minimum. The reason I know this is that he has done that every season since he has been a coach at MSU. I don't see that changing. Anyone that thinks that the MSU offense is served best with Russell running the ball that many times with his career 2.3 ypc is simply not thinking correctly. Now I think the MSU offense can be fine with Russell and Prescott splitting time at QB. Now this is good for MSU, but sucks for Russell, but who cares as long as MSU is playing well. At the end of the day, Russell is not a good fit for MSU's offense, that doesn't mean he isn't a good QB. Eli would be a terrible fit for MSU's offense, so would Aaron Murray or Tyler Wilson. The kid clearly loves MSU and wants to see what he can do and maybe he is a tougher runner than he has shown in the past.