The majority of Noel Hill's pupils is more likely to be in Ireland and most certainly not isolated from the living tradition.
I don't really get the notion of professionals 'developing' existing styles and taking them to a higher level. You could successfully argue Noel Hill 'developed' the style invented by Paddy Murphy but I don't think it would apply to all 'professionals', they're traditional musicians: part of the community and not necessarily 'higher developed' than some not wearing the 'pro' tag or those with a lesser urge for venturing out into the world.
And I apologise for going on about this but I really feel this is not a music of 'professionals'. There is such a number of wonderful players who are mad for it and play lovely music without all that hooha and hype.
I entirely agree with your final paragraph. One of the things I value about folk music is that sense of involvement at all levels, and that there are so many wonderful musicians. I also value that the majority of the well-known players, professional or not, remain rooted in the tradition and that both amateur and professional players find it quite natural to be playing alongside one another.
Ireland is undoubtedly fortunate in having a strong living tradition and developing players are not isolated from this. But Noel Hill, for example, give classes all around the world, and many of his pupils outside Ireland will not have the same opportunity.
For myself, I had been involved in folk music for more than 10 years before I came across a "source" musician. I had unthinkingly bought into the widespread assumption that the English tradition had more or less died out at the time of Cecil Sharp. All my early influences were revival musicians, with the sole exception of the William Kimber LP. Now I have much greater access to traditional sources, both recorded and live, but the professionals remain my biggest influences, especially regarding instrumental technique.
There is a small group of people who have chosen to make a living, or part of it, from folk music. There is a much wider group of equally competent musicians who for various reasons have chosen to make their livings in other ways. I'm not saying the latter are any less important, simply that their sphere of influence is smaller - they play to fewer people and are geographically more restricted.