I've flown with a WIDE variety of individuals in my 32 years of flying! I've also flown with a wide assortment of gender and ethnic backgrounds mixed with just about every training background known including military and civilian. I've instructed in everything from a C152 as a newly minted CFI to widebody jet IOE and sim instructor in my airline career.
I can usually tell within the first 5 mins of a flight what type of airman I'm paired with without knowing their background. First, I've learned to be very wary of the individuals who verbally recite their resume to me on the initial handshake. Second, I've learned that someones attitude tells me a lot about someone's flying ability. A piss poor attitude usually precedes a piss poor performance in the airplane. Third, Someone's flying background doesn't necessarily tell me what kind of airman you are or guarantee your "ace of the base" abilities in the airplane. Fourth, don't tell me...show me how good you are!
I've said it before that time in a logbook does not always correlate to ability in the airplane. I've flown with some very good low time pilots and some very bad high time airman. In general, the higher time folks tend to do a better job especially when things don't go as planned which is most of the time.

They have the experience and judgement to adapt to new situations more easily than a low timer.
The only folks that think a 300 hr pilot is qualified and experienced enough to pilot a jet full of passengers are the 300 hr pilots themselves. Yes, technically they're probably right, they can get the airplane in the air and back on the ground.....as long as things go as planned. I wouldn't mind the 300 hr right seater near as much if I knew the Capt in the left seat had more than just a couple thousand hrs!
A 300 hr wonder in the right seat is kind of like my teenage daughter telling me she is old enough and prepared for all contingencies when she wants to go out alone with her friends on Friday night. As soon as I quiz her on her "what if plans" her thoughts begin to look like Swiss cheese with a lot of "I don't know...it probably won't happen anyway". So, while technically she is old enough to go out alone with her friends, she doesn't yet have the judgement and experience enough to see and avoid potentially dangerous situations.
In a perfect world most folks would agree that all airline pilots would have at least 10,000hrs and have a little gray hair to boot, much like their surgeons. I thought I knew it all when I was a 21 with 1600 hrs. 27 yrs later and I feel like I know less now then I did back then. I guess that's only natural as we age and become a little more cautious and feel a little less bullet proof. Even though I was a young 21 yr old "kid" when I first got hired by a commuter airline, I thought I was well qualified to be there. You know, every kid thinks they're well qualified to drive at 16 and know everything there is to know. I've since realized just how much I really didn't know. I realized how much I relied on my more experienced Capt's to keep me out of trouble until I had a chance to learn the lesson. I've realized I was initially more of a liability than an asset to these Captains even though most took it in stride and taught and mentored me along the way.
While I personally (and it's my opinion only) don't believe in these fast tracks/low time programs to the right seat of RJ's, most *eventually* become seasoned veterans and very good pilots over time. It's simply human nature to want the most seasoned and experienced pilot flying you around. Everyone wants the most seasoned and experienced surgeon if they ever need those services. To say otherwise, well..you're only kidding yourself. It's the time between 300 hr to experienced aviator I worry about.