The problem isn’t the platform, it’s the people. If mastodon got as popular as twitter the level of discourse would fall to the same level.

Popularity in itself is no problem for any platform, as long as it manages to scale up moderation together with growth. CSAM spreaders and ordinary spammers are the least of the worries thanks to AI and other automated detection systems these days, but warez/moviez are harder due to the DMCA and European fair use laws (e.g. German §51/51a UrhG), and stuff that veers into anything politics absolutely needs human intervention.

HN is pretty decent at that, despite it (IIRC) being only Dan (u/dang) doing the moderation work. (Maybe it helps that both the HN tech and the general community itself don't make it easy to post dank memes like on the other social networks)