The way it's supposed to work is that each user would view this from their own Mastodon instance, and the federation would mean that traffic would be much lower

The way it's supposed to work is that each user would view this from their own Mastodon instance, and the federation would mean that traffic would be much lower on the source instance. That doesn't work when people post links like this though. Maybe we need something like activitypub://@username/postid that can be opened in the user's default client if they have one, or could be resolved to the original instance if not via webfinger. Unfortunately never going to happen, but it would be in the spirit of the systems.