@ernest The thing that's different from email for social media is moderation, which is why the host matters. Also, for both email and social media, the host matters for other reasons: you don't want someone who's going to lose all your email by going out of business suddenly, or who has poor uptime, etc etc.
Saying "the host doesn't matter" caused a lot of people to bounce off the Fediverse when they first tried it, because they wound up on hosts with terrible or no moderation.