This! In many ways shared reviews for SKUs of the same product make absolute sense (if the blue bag is made well, so should the red one). But there seems to be huge abuse in defining the base product as you've highlighted. I presume sellers have complete autonomy to set them up, and Amazon might argue that it's "infeasible" for them to administer this, but from the perspective of the consumer I completely agree that it erodes confidence in "reviews".

Over the years I've noticed a shift in the products I most readily find on Amazon from well established brands to utterly unknown Chinese manufacturers. I've been burnt enough times by buying such products that I've reverted to mostly looking for products which satisfy 1) from reputable company, and 2) positive reviews.