Google Translate:
First of all, the ActivityPub system is not suited to something like Misskey, which flows at lightning speed.
It was originally designed to connect blogs, small-scale SNSs, and wikis.
How can it handle the TL hell where tens of thousands of requests fly in per second?
It’s based on the idea that it would be nice if various small services could send each other updates, so it’s quite costly.
I think the main alternative to Misskey is its fork, Sharkey? I’m not personally familiar with them though
I think misskey.io is the flagship instance for Misskey so they would not switch since it’s their own software? other instances might
There are several, this is an overview and it’s probably outdated: https://pancakes.gay/misskey-comparison/
Uh sorry, I was a bit unclear. I meant their alternative to leveraging ActivityPub for what they do.