Content mirroring will be a big problem

Few days ago I discovered that any time you follow a fediverse account on a different instance than your one, the server you are on mirrors the original content of any toot/post, and I think this is a huge issue, because then every Fediverse server/instance could quickly get overloaded from contents from other servers! Am I right? I've always thought that toots/posts from other instances were just "empty shells" retrieving the content on demand.