There have been top coordinators who have failed and succeeded, coaches from the G4 and FCS level who have succeeded and failed and even successful P4 coaches who have succeeded snd failed. There is no magic solution.
In recent years, G5 coaches who have transitioned to success at the P4 level:
Josh Heupel from UCF to UT
Kellen DeBoer from Fresno State to UW
Curt Cignetti from JMU to IU
There is nothing that says Sumrall is an automatic home run hire. He might not succeed at the P4 level, or he might kill it. I’d rather find that out with him doing it at UK than another P4 school because I think it’s worth the gamble.
That's all I am saying, success at a G school doesn't guarantee success at a P4, and same for a coordinator from a P4 . Even success at a P4 may not get the results one is hoping, look at Mullen.. But if a program has stalled, the only option is to make changes and hope it's in the right direction.