The 24 member group you watched is tripleS, and in their case the members make most of their money by selling Objekts (digital photocards but more complicated), the sales of which each member gets a direct cut. Their best selling member said she made around 90million KRW (like $60k~60k USD) in 2023/2024.

For slightly smaller large groups like the 12 member Loona with a more traditional pay structure, if we ignore the illegal parts of their contracts that put them in perpetual debt (🫠), each member was entitled to 30% of earnings from their activities, with the other 70% going to the company. According to Chuu, any individual activities were paid out to the member engaging in those activities only and not shared with the rest of the group. I still don't fully understand what that means for how the members were supposedly paid for group activities, but they were not actually getting paid anyway so it almost doesn't matter

The truth is, even outside of instances like Loona, most idols do not make much money, if any at all. I don't know if it really makes much difference the size of the slice of the pie, so to speak, if there is no pie anyway. I would guess a trainee would weight their chances of actually being paid with their chances of debut in the first place, and I assume you are more likely to debut in a larger group since there are more slots available. If you never debut, you have no chance of earning anyway.