@mttaggart good list, but I don't think it's fair to Matrix today.
The CSAM attacks happened, but moderation tools have taken a big leap since. You can quite easily use a moderation bot that subscribes to public ban lists. This almost fully ends any generic spam.
Also you talk about matrix.org as "flagship server". Friends don't let friends use matrix.org. Use small/medium sized servers instead and you get better performance. Same applies to Mastodon - don't use mastodon.social, decentralize!
My main criticism would be the buggy mobile clients, and super slow migration from Element Classic to Element X. Element web/desktop are decent quality, but far from polished.
Oh and you don't even mention bridges. Other alternatives don't even try to support them. Bridges are a key feature.