There is a drinking culture in rugby union amongst younger players, sadly driven in part by parents who set some pretty bad examples. That was one of the reasons I was not particularly bothered when my son quit club rugby a couple of years ago to concentrate on swimming. Swimming is tough, but they do bang home the message about lifestyle continuously. Way more than in rugby where diet, sleep etc was barely mentioned. I must have sat through 5 or 6 nutrition talks directed to parents in 3 years of him swimming, sleep, school were all discussed frequently. I heard from a mate whose lad plays for Bath that when they go on tour without parents (U15) they will drink.
Swimming is all about small percentages, if my lad had improved his times by 4-5% for his 100's and 200's then he would have gone from regional to national qualification. Another 1-2% and he'd have been national champion. Players like Sinfield, JJB, Peacock, McGuire, they all know this applies to rugby as well. Inches separate getting into the right position to make a tackle and the wrong one and a missed tackle can cost a championship.
I can't comment on league, I have no experience of it at junior level but I do wonder why a lot of our academy products over the last 10 years have not made the grade with our first team and those that went elsewhere, although seemingly talented, seem to lack consistency to really make an impact on the game.