"...were having a MUCH higher washout rate than the 250-500 hour pilots coming into the airline with airline-specific training..."
Yeah, I hear that one all the time. There is no doubt that the RJ course will help the 250 hour, or the 2500 hour, guy get through 121 ground school and the sim. I mean, if you've already seen it once, it makes it easier the second time. What the RJ course doesn't do is make you a better pilot in the way being a CFI would. Skills you get as a CFI have more to do with judgement, self confidence, and good CRM, than stick and rudder. These are important blanks that the 300 hour F/O can't fill until he's working as a Jet F/O and I simply don't think it's appropriate to bring that experience level into an airline cockpit.
As far as the "must have been a CFI argument". I agree that's it's not for everybody. I've heard countless times, though, "I didn't think I could do it but once I did it was a great experience". That should speak something to those who have yet to experience it. Food for thought.
Also, I'm not saying "everybody has to be a CFI" so much as defending that the CFI is a great way to build useful time and is not a waste nor worth the effort. There are other ways to gain some minimal skill level before heading for the shiny jet.