Well, the good news is that at least some of those that sort by new/all know that the newest version of a repost is the newest, and that the last one is the earliest.
The issue you're raising is one I've had conversations about in meat space.
The problem with that is that not everyone who knows about it pays attention to it, or bothers to report things since it would require scrolling back
Personally I rarely report because I have no way of knowing if a link came independently or via repost. It's easy to spot when it's something like a meme or similarly identifiable, but even then it may not be intentionally douchey, just thoughtless. So reporting isn't necessarily a primary option.
I don't think there's an easy solution to the problem tbh.