Automatic curation doesn't have to be on the server side, much less by a centralized authority. An ML curation model won't even need the processing power used by client side LLMs these days.
All that said, my experience with mastodon is the opposite of what you described. I find the chronological feed to be always interesting and much less frustrating and emotionally draining than any curated feed that I know of. Members are a lot more considerate too. From the discussions there, I know that there are a lot of others who hold the same opinion.
I'm also in small online communities where people are well behaved and threads are high-value and on-topic. But these are side effects of being small, and are unrelated to the tech involved.
Mastodon seems high quality now only because "no one" is on it. It's currently self-selecting like minded people who are invested in making it work. Add a million people a day for a year and see what happens.
No community survives the eternal September.
The mistake is in thinking that the -tech interface- matters. It does not. The size, and quality, of the community directly dictates the size and quality of the content.
All that said, my experience with mastodon is the opposite of what you described. I find the chronological feed to be always interesting and much less frustrating and emotionally draining than any curated feed that I know of. Members are a lot more considerate too. From the discussions there, I know that there are a lot of others who hold the same opinion.