The only sporty YouTubers I follow are in parkour and World Chase Tag. Most of those are demonstrating their own skills, so they do have to be good at what they do. Some are among the best in the world at what they do. Only one (JimmyTheGiant) is mostly commenting and interviewing (and making brief documentaries about the history of the sport), and he's open that he's not the best at the actual parkour.

I suppose it depends on the field. A retired athlete probably still has a lot of useful things to say about their sport, whereas other fields really require you to stay up to date to be useful.