The music industry seems to have a pretty good solution for this.
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.
So media tycoons are getting washed up, rather than getting continued returns?
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?
A musician might be risking their entire livelihood; an investor risking a percentage point on their portfolio's annual profit. Bonus points if the wealth was inherited and is managed for them. Your claim just isn't true as a generality.
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.
I'm not talking about personal risk, I'm talking about risk of loss in absolute value, i.e. the investor is risking more capital so they claim a bigger share of the reward.
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.
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.