I mean I'm watching Bettel and his sea of supers/gifted members and
Would you rather make 80% of 500 dollars
or 20% of 5 thousand dollars?
And I seriously doubt that they'd go as high as 80%. From what I've seen Idol hasn't really inspired massive donation waves, vod rewatching (for ads). They got Raid shadow legends, sure they probably made some money off of that. But lets not kid ourselves. Outside of Rin, Idol doesn't seem to be that big at the moment. Not big enough for those with an opporitunity to join Holo to stop and join Idol instead.
I would say Nijisanji as well, but I'm not as familiar with their numbers and merch, this isn't me kicking Nijisanji when they are down. They could very well also be a more lucrative opporunity for new recruits despite bad percentages. Idol does however provide equipment and games, so the starting point I could see would be much more enticing, as long as the talents don't compare the math too close.