I see a lot of assumptions that ad support lowers the quality of the product.

There are two obvious historical examples to look at:

1. Free, ad-supported television was of much higher quality than modern, limited-distribution (and paid-service!) television.

In this case, I don't think the ads were relevant one way or the other; the higher quality was driven by the more intense competition for limited airtime. Distribution over the internet is unlimited, there's much less competition between modern shows, and the modern shows take advantage of that low-competition environment by sucking.

2. Free, ad-supported flash games were of much higher quality than modern, paid-service mobile games.

Here the ad support is clearly causal to the higher quality. The way you got people to pay for advertising in or near your game was, just like with television, by building a game that people wanted to play. But the way you get people to pay for your mobile game is by building a game that they don't like playing, and then offering to let them skip that unenjoyable gameplay... for a fee.

https://foxtrot.com/2014/03/23/candyfarmdungeon/

So it's not obvious to me that an ad-supported product is necessarily bad, or even worse than it would be without the ads.