Yes, the opportunities are huge...and they have to be to attract new money. I don't know about equties, but in futures every winning contract has a offsetting losing contract. If the winners in any given year represent 20% of the players as in a pereto-levy distribution then the opportunity must be very great to attract people that appreciate the odds.
For instance, for a person in a deadend 50k/year job to take up trading with a 80% chance of breakeven or loss in a given year the payoff must be 250k or more (otherwise the person shouldn't trade). (.2*250k) - (.8 * 0k) = 50k (actually the trader needs to make more due to higher taxes, and paying their benefits out of pocket).
Fortunately, I don't think the winning years are independent. My experience has been that a win in one year tends to predict a win in the next year. Unfortunately this also implies that a losing year begets a losing year, so the odds of a losing trader joining the 20% club are pretty slim.