I have similar issues on a site I’m developing. I think @herry is onto something.
Why not create a simple mechanism for lazy loading repeater items on request?
This could be activated using a filter and would hide all of a repeters fields until a “show fields” link is clicked.
This should be pretty easy to implement and we would be able to stop ACF from loading and saving hundreds of files every time a page is edited.
It would solve all (most) performance related problems that backend users are experiencing due to having to many repeater (or equivalent) fields.
