The expected ROI is actually much more complicated than that, but even with the numbers you've suggested, $8K and no time to make $35K is a good return. $0K and working at it full-time to make $65K is a job. The person who invests the $8K will still be able to work their regular job or business, the pool player won't be able to if they want to give it a serious go. The only way the player has all to gain and nothing to lose is if their time is valued at $0.
By the way, while we're on the topic of ridiculous analogies, there is no logical way to compare this to a real estate deal or a stock trading deal where the player would get a commission of 6-15%. Neither party is an 'agent', they are both 'principals' in the deal.
A better analogy if you don't like the one about horse breeding is where someone needs some money to get a newspaper stand started so they take on a silent partner. During the course of the next year, one takes on the financial risk and the other takes on the time, effort and day-to-day responsibilities of the business. Both parties share in the profits or suffer the failures according to the initial agreement.
Cheers,
RC