The API fees clearly weren't made to make money directly though, it was meant to get rid of 3rd party clients so they could more effectively do what the OP is about.

I bet the they lost single percent of people. And most use it and don't care.

We don't know their actual engagement numbers, what I do know is: quality on non-default subs has pitfalled. That is subjective, but its common across other reddit users I know.