> I can imagine that these are being recorded on a high level

Isn't that just another product backlog by another name?

> only deep-diving into it, breaking it into smaller pieces, when it’s on the radar to be picked up soon.

This I can agree with. Wasn't that the original intent of User Stories anyway - a promise for a conversation about this feature or need at a later time?

For what it's worth I agree with you that a too-deep backlog is a problem. I'm just not sure that you proposed any solutions to this problem?