Nil Further - I will try to answer your questions fairly
Yes, the limit for a dash command in Flybe is 2500 hours
In the past (actually prior to 9/11) a few commands were given to pilots with less than that experience (I believe there were three of them, but stuck as I am on a rock I may have missed one or two)
No there was nothing to stop them flying with a new F/O provided he had at least 100 hrs on type.
However, none of that is relevant to your statement - "a lot of inexperience in Flybe". You could have said "two years ago there was some inexperience in flybe", with that I would have had no argument. Or alternatively you could have said that "in common with almost every scheduled carrier in the UK, including easyjet, flybe have crews less experienced than those in Virgin/BA" - that I also could not argue with. But your original statement could easily have been taken by anyone less informed to mean that Flybe were exceptional in this area, and I don't think that is the case.
All that aside, that was then and this is now. Since last years pay settlement there has been a lot lower turn over in pilots at Flybe ( I am not saying that things couldn't change in the future, mind) and there have only been a couple of promotions on the dash in the last 12 months, plus jet pilots coming onto the aircraft ex 146 and CRJ. You won't find experience levels anyway near as low as those that existed in the past on the dash 8 200/300 on the flight deck of the 400s.
Also of course all of that had no bearing on this incident, as I have said. The captain of the aircraft was highly experienced, although not familiar with the peculiarities of runway 15 at BHX - and the briefing pack he received from the NATS briefing system at EDI made no mention in notams of "slippery when wet", nor does the AERAD airfield booklet.
I will however apologise for my use of the word "alleged", re-reading your post I notice that that part was actually referring to times gone by, unlike the rest.