First, I would like to know - are there any authoritative studies on this topic?
Do bookmakers or prediction platforms themselves publish statistics on the percentage of profitable players in relation to all other players? Does this information differ between different sources? Is there a difference in long-term profitable players in bookmakers and on prediction platforms?
There are no authoritative studies on this topic. This is likely your cue to become the first person to do one. It is going to span across several countries and several years for it to become an authoritative studies. Bookmakers will not do it. It is out of their scope. You want people to gamble and not give them the impression that they'll lose even before they make their first bet.