I found this screenshot of the partner program contract that says it's a 55% split for either https://imgur.com/YjOHAAr
But for Premium the amount is distributed by watch time, whereas for ad-supported users it's by number of ad views. This means that for short videos where the value of the ad is higher then the value of the watch time, a "free" user wins, but for longer form videos where the watch time is longer, the Premium user wins.
LinusTechTips once showed the YouTube income breakdowns for some of their videos that showed this - for their hour+ long PC build streams, Premium income was higher and for shorter videos, Ads income was higher.
But for Premium the amount is distributed by watch time, whereas for ad-supported users it's by number of ad views. This means that for short videos where the value of the ad is higher then the value of the watch time, a "free" user wins, but for longer form videos where the watch time is longer, the Premium user wins.
LinusTechTips once showed the YouTube income breakdowns for some of their videos that showed this - for their hour+ long PC build streams, Premium income was higher and for shorter videos, Ads income was higher.