I don't think Raymond Mulgrew really wanted it enough, Coney was pretty honest in an interview a couple of years back that he didn't work hard enough or apply himself correctly in his early years on the panel and thought that his talent alone was enough. Ronan O'Neill just didn't have the physicality to show it at senior level and had a very serious injury at 19.
I think people underestimate how difficult it is to do what Conor McKenna has done, go over at 18 and take up a sport he never played and excel at it. You probably have around 10 GAA players who sign a rookie contract on an annual basis. There's only really 4 well established players plucked from the GAA, Tuohy, Hanley, McKenna and O'Connor that are regulars or key players. I think you have a few guys like Nash, Glass and O'Riordan now who might be making a breakthrough too but the % who succeed is very low and I have absolutely no doubt that if the likes of McKenna or O'Connor returned to their respective counties now they'd both be absolutely key players for them and be likely to be in the all star hunt. Hanley and Tuohy are unlikely to come back at this stage in their careers with both in their 30s.
Clarke and Kennelly are the only two players who returned from the AFL after making it there and both proved themselves on their return as key players.