Insinuating that you cannot be a "rounded senior instructor" (whatever that is) without a background in airline or RAF flying is simply not true. I know many civilian instructors from various backgrounds that are very professional and constantly looking at ways to improve themself as instructor. End of the its down to the individual and how that instructor is managed.
You've shot yourself in the foot there! If you dont know what a 'rounded senior instructor is' how could you understand what I am insinuating?
However working on tbe assumption that you do indeed know exactly what I mean:
A wide ranging experience also allows you also to understand that we all have different views based upon our own experiences. Your assessment of 'very professional' may well be very different from mine.
In regard to self improvement, the majority of self improvement that instructors seek is in fact moving to an airline. I f you dont believe me go onto any airfield and ask an instructor if he would rather earn his living on an Airbus or a Cessna 152!