You’re relying on a lot of assumptions, which even if true, still doesn’t mean that the math works out in a way that means allowing ad-blocking users makes sense.
Netflix doesn’t need a “healthy community” for people to use the platform. Shows do perfectly fine letting all the talking happen on other social media.
AND you’re assuming youtube wants to continue the already unsustainable ad-based model at all, which with how hard they push premium, definitely isn’t the case.