I put together a dataset of various streaming service library sizes the other day, just for fun. I got the data from going to justwatch.com and clicking on individual providers in the US.
Here's the page I used for that.
The only service I use regularly that I don't have numbers on is Pluto. Also, to get Amazon numbers I added Amazon Prime and IMDBtv Amazon numbers together, because Prime is free with prime, and IMDBtv is all the stuff that's free with ads. Amazon Video is digital rental and sales titles, which I'm not interested in. The largest libraries on justwatch are digital rental and sales libraries, but I never use them. I only use subscription or ad based networks.
So I've been browsing over these services, and thinking about what makes a good streaming service. I don't think it's library size, although library size does help. I love surfing Tubi. I consider Vudu to be lower quality than even Disney+, though. Peacock's free tier is more impressive than I expected it to be. I might drop HBO and go to Peacock.
Remember when we thought Disney+ would dominate because they bought 21st Century Fox? Ironically, Tubi is owned by Fox Entertainment, which is made up of all the stuff Disney left on the table in that deal.
Here's a cheat sheet for where the old big 4 network content is now:
ABC: Disney+
NBC: Vudu, Peacock, (NBC also has a minority share in Hulu)
CBS: Paramount+, Pluto
Fox: Tubi, Disney+