I have no idea if Steve Coombes was direct entry or a former assistant, but either way, he should have sufficient GSK to understand that such a letter is not appropriate.
I don't think it fair to compare the direct entry Pilot Officer doing JATCC with a direct entry Sgt going there, as the IOT element is the best part of a year before getting to Shawbury.
A huge part of being a Sgt controller is being a leader, as well as being a controller. The SNCO bit is not just a badge, and perhaps more emphasis needs to be placed on "Sgt qualities" when the selection for JATCC is being made.