I recently posted a link that got 2 boosts and 6 faves, but it was requested by about 300 fedi servers so they could generate a preview.

Which is fine! Because even though my photo gallery runs on a 15 year old laptop in the basement, I wrote the gallery software in a fast language (Rust) and so a trickle of requests maxing at 4 per second is not actually a problem.

People complaining about fedi hammering their servers are probably using PHP or Python.

not the parent commentor, but I've previously heard complaints about how each server separately does a fetch of images and html for previews.