There's no moderation because signal groups aren't 1:n they're 1:1.

The protocol doesn't even guarantee everybody in the group sees the same message.

This is wrong. The group admin knows the list of messages, so they could send a message to all the participants saying "remove this message".

The fact that they are 1:1 means that the server does not know about the group, but quite obviously the group knows about the group.

Your just like wrong man.

Nothing even says the admin has to get the offending message.

people can see reactions :p they can also see when a mod adds or demotes a member