Sounds reasonable to me... I am sure sites like sharkscope (despite their faults) have a reasonable amount of data that could support this claim. Also, I am sure poker sites have some data that may support this general claim. But The Truth Is, nobody really knows, as Nobody Has All The Data On Any Player... So it is anyones guess.
If nothing else, at least there is a percentage of players that only play Freerolls and other Free Tickets, and otherwise play very responsibly that are Winners... So The Real Question Is... wait for it....
How big a percentage of that 5 - 10% of All Winning Players are CardsChat Players?
I am pretty sure we have quite a few...