I'd go B+/A-. It's a home run given the shape the program is in. He bring the exact offense most of us want to see, and had a top-10 offense this year at SMU. Wouldn't go A though since I'm not sure he'll be a greater recruiter or bring in a great OL coach.
Honestly this is similar to USC hiring Harrell. It definitely gave their offense an identity and they were much improved. Lashlee should be able to do that here.
HOWEVER, like USC, we have structural issues as a program and a HC who isn't qualified. Even with an improved offense I think our ceiling is 9-3, with 8-4 being more realistic