I don't see how that ratio thing could be enforced on a protocol like ActivityPub, it would be an instance-by-instance thing and people from instances that weren't enforcing it would be able to downvote however they liked.
There are instances that blocked downvoting entirely (beehaw.org, for example) but when I saw threads from there here on kbin.social there was plenty of downvoting on them from non-beehaw users. Only on beehaw.org would the threads be seen downvote-free and would users be prevented from downvoting on them.