This should be a client-side fix, not a nostr-level fix. For example, the note IDs and pubkeys of reposts could be stored locally for an hour or something. The client should only show one repost for a given noteid during that time, with all of the reposters listed. Then after an hour it could be cleared so that the next repost will show up at the top again.

Just spitballing, but something like that.