We can look at PeerTube for an example of a system that could be shaped into what I meant: when you look at a post (video) from peertube it links lists for likes, dislikes and shares (so basically upvotes, downvotes and boosts). These collections contain a totalItems property, but also list the peoples identities, but just imagine that it wouldn't be there. When a user now likes the video, the creator of the video now sends out an Update acitivity to all subscribers. Now all subscribers can update the counts for likes, dislikes and shares. Only the "home instance" of the creator account knows about all votes, nobody else does, but nevertheless everybody else can now how many likes, dislikes and shares there are.

If we compare that to mastodon the first part of the statement is still true:

Only the "home instance" of the creator account knows about all votes, nobody else does

But that means that most instances just show 0 likes for most of the posts, because your instance only knows about likes originating from your instance...

As for your proposition: I couldn't follow for some of it. However I think the risk of an actor abusing the creation of fake accounts and fake upvoters is not really a risk, that is what defederation is for... I would argue very much agains a lemmy specific protocol and some judge instances simply because then big instances would just have pretty much all the data again and it would definitely hurt interoperability because lemmy devs can then just take the easier route instead of implementing something according to AP spec