The performer gets a cut. The lyrics writer gets a cut. The melody writer gets a cut.
I'm sure something similar could work.
I'm also recovering from just finding out that the process I thought happened behind artwork was largely false, and has more in common with renaissance painting businesses than the title artists work.
No, of course not: this is why we've had ever increasing numbers of sequels, remakes, franchise films and such. Why lots of heavily promoted music is highly derivative.
Sure, some people invest in riskier stuff, on the hope of much greater returns.
What are they risking, will they suffer in any meaningful way if the project fails?
Their exact cut is generally a balance between the risk, reward, and ability of the venture to happen without them.
Risking the largest absolute financial input is not equivalent to having the highest risk unless you exclude all human value, and consider a dollar to be of equal value to all people.
Bigger musicians will fetch high prices and in some cases, take on the financial "risk" (almost none since they're a superstar) themselves.
Also, its not like a single bad song is going to ruin a career. Clearly you haven't heard an album from the front to the back if you think that.
If the musician was able to provide enough capital/resources on their own by risking their entire livelihood they'd have no need for an investor and could take the entire profits of the venture for themselves.
I'm not making a moral judgement here, I'm just saying that it's a fairly straight forward logic as to why people who "only contributed financing get a bigger cut". The OP is wrong to claim they get a bigger cut because they're already rich, they get a bigger cut because they're risking more capital in the venture. It is secondary that them being rich means they have more capital available to take risks.