Heights makes some good points. It is a question of supply and demand and that changes all the time.
Certainly different skill sets are required for different types so it is not really horses for courses. Without being rude, there is an entirely different skill required to fly for 8-9 hours with a fairly low arousal state and then 30 minutes of terminal activity compared with a 30-40 minute arse on fire routine.
It is also true to say that many a V-force copilot, once the requirement for a previous operational tour had been dropped, were posted to V-force as they were deemed not yet ready to operate as a 1st Pilot/Captain. It was a long standing complaint that the Vulcan was a 4-engined extension of the jet Provost. It was also true that many flight sim instructors were ex-Herc copilots.
With a large in to service requirement it follows that the full range of aptitude skill levels would get selected. With fewer seats it follows that those being selected will all be nearer the top bracket.
Certainly there was a thought to post weak navs to GR1s where they would make or break quicker. Don't know how many fell in that bracket though; it was probably something inspired from the Buccaneer mafia (you'll know who I mean if you were around in the late 80s at ANS - later joined BWoS).