the rank of Sergeant was never a controller
Not only do they have Sgts as controllers, there is now direct entry as such, not just the cream of TG 9.
Personally, I have no difficulty with this: for years we have had direct entry SNCOs as aircrew, and for even longer direct entry controllers as officers.
So if (perhaps a big if!) you can accept a 20 y.o Plt Off controller, and a 20 y.o. SNCO Chinook loadie, then what's the big deal about a 20 y.o SNCO controller??