CBS All Access used to sort of do this (before they become Paramount+). I used to watch on their site (CBS.com) without an account nor sub, for free (but episodes did expire). IIRC, it was roughly 8 minutes of commercials per 1-hour time slot of TV (so around 42 to 54 minutes of actual air time). I heard their $7/mo plan with limited commercials was indeed half the duration of commercials. Don't know if anybody does that anymore. Perhaps Peacock since they have 3 tiers? However, I think the only differences between their basic and Premium (middle one) tiers is Basic is free, limits the # of hours you can watch per year, and not all of the full content is available. They're both still the same amount of ads.
It guess it depends on the streaming service (ss). For example, Hulu w-ads when it was only $1 per month (via Thanksgiving/black Friday promo) makes far more money than Hulu ad-free at $13 per month. To the dismay of Hulu users, this is why the latter is never discounted 🙁
You do have some "lesser" ss like Freevee and Peacock basic tier (the lowest one) that are free, and completely ad supported. YouTube has always been free (although I'm glad I was able to get in on a YouTube Premium family plan, as I could swear they doubled the amount of ads in recent weeks).