I think there are a number of factors that go into what becomes known as a "typical" P-51 pilot. I think first off to an U.S. player it is the most iconic aircraft of WW2, anyone with even a passing knowledge or familiarity with the air war will at least recognize the P-51, if an allied plane is going to appear in just about any WW2 based game the 51 is more the likely going to be included. It also has a reputation for being a war winner, so if you're a new player the 51 will probably be high on your list of planes to try out. It's the best right?
One thing that just about every player has in common, we want to be successful in whatever part of the game interests us. So we have a plane with a sterling reputation (some would say historically overrated) so they take it out, and quickly die. So they start asking around, how do I get better at shooting people down in the 51? What's the single most common answer? Don't slow down, keep it fast, BnZ, for a new player who hasn't yet developed a sense of ACM, much less aggressive E fighting (which I think is one of the harder skills to teach/learn) this advice quickly becomes the one pass, haul a** P-51 pilots we see all over the place in the MA.
Does the 51 breed "sucky" pilots, no, I think the community does to a large extent.
Now that's going to sound pretty critical, but I don't think it really is. What does the 51 offer the neophyte AH'er? A plane that offers good survivability (it's fast), a good ordnance load to help take a field (dive bombing is a more easy skill to teach and develop than complex ACM). In short it gives the new player a chance to contribute in some fashion and maybe not get slaughtered in the process. At the end of the day that's all each of us is really after.
Do I get frustrated by 51's who don't engage in a fight? Absolutely, but I can say the same about 190's, Typhoons, La-7's.
Naturally this isn't going to apply to everyone, we have aggressive 51 pilots, we have less aggressive vets as well who for one reason or another aren't interested in a protracted fight (I do think a 51 can be flown to it's strengths and "fight"). Admittedly it's a generalization with a lot of exceptions but when you look at the overwhelming presence the 51 has in terms of number of sorties I think this covers a lot of it, at least in part.