I'm very late to this, but to make a review system for plugins valid you have to have a regression to mean.

i.e. the older your review, the closer its value gets to mean. So if you made a 1 star review of a plugin five years ago it's value today would be 2.5 stars (assuming an equivalent 5 star review from the same period).

So a good and frequently updated plugin would get a continuous stream of good reviews, keeping higher stars than a good plugin that suddenly stops getting updates.