There are many traders who have succeeded in making a profit in their trading sessions, but it is difficult to find the exact percentage considering there is no data to support it. I think the comparison between traders who make a profit vs traders who lose doesn't have much of a gap, the percentages can be very close because when others lose, there are those who gain.
That's correct when you said if someone lose money someone gains, But this is where you get it wrong mate!, it doesn't mean the gains are widely distributed that everyone has to profit at same time, the money enters in the pockets of few traders who understood what they are doing in the market, especially the banks ,the hedge funds, institutions and market makers, they're the one that most of these money ends up in their bag, now think about this, out of many traders you know, how many is actually profitable?
When about 95% of traders lose money, how many traders are then profitable?
You think there's no data? brokers has data or records of their clients and monitors their profitability.