I have found out the percentage of gamblers that are losing before, but I have seen sites that said 90 to 95% while also some said 3 to 5% and some said 4% and so on. What I noticed was that almost all gamblers are losing.
I do not think that is a long term estimate because if it is long term, I guess the percentage will be less than 4%. This is not what we should bother about unless will have something to write about it like a project or news or something like that.
I would say the same thing that the percentage of long term winners would be at 3-5% since as you have said that almost all gamblers are losing and even if some gamblers did win yet they would still use portion of their winnings or even gamble it again next time so, that's probably the reason why casinos and bookmakers are popular and also why there are many newly made casinos and bookmakers that are popping up even here in the forum.