It doesn't cost much more to operate a Q400 than a Q300 or Q200 for that matter.
It'd also true that you can fill any aircraft and lose money, and half fill another and make profits.....how to do the latter is the secret of commercial departments the world over, well one they well know in Exeter anyway.
Rumours can occur for both water testing and disruptive reasons, often, they're just pie in the sky.
Simple logic tells me a route that succeeds on a 19 seater, that doesn't impact on close by major route's are neither a threat nor an opportunity.
As you say, Horses for Courses.