@helgek @darnell @nickapos @jan

No! You have it wrong, and your error is exactly the point here!

ActivityPub specifies that every post should be delivered to different instances following that post, so no, if people post twice as much you should NOT expect twice as much traffic. You should expect traffic to grow by number of posts multiplied by number of followers, which feeds back into number of posts, which makes the traffic requirements not so simple!

These are exactly the scalability issues that I noticed when I read the ActivityPub standard.