"5 Star" ratings are numerically equivalent to 20% (or points) per star. "10 star" rating systems are rarely used, with one oddball being IMDB. (rows of 10 stars, simply take up to much space to be practical).
However, cumulative rating are pure mathematical averages, of the number of different "star" ratings received.
Whether I'm shopping or reading a review, I attempt to psychologically evaluate the buyer or reviewer's abilities and/or motivations for the mark received. At the extremes, motivation by compensation for a given product. So, "5 stars" is applied Or, the complete inability of a buyer to use and understand the intended purpose of any given item. In the case of a buyer being a complete imbecile, this would net, "I'd give this piece of sh!t mo stars If they'd let me.. After which come the realistic appraisals from knowledgeable buyers.
Then there comparative reviews. For example, comparing a GTX-1630 to a GTX-4090 might give the 1630 1 star, and the 4090 10 stars. (Assuming the 4090 didn't burn down the reviewer's house).
As for your level of education, I'll refrain from making a guess. You might be studying for you masters in social Psychology, but suck at math. Or put differently, (and more tactfully), math might not be a priority in your career objectives.
However, math is a concrete science, and terms like "subjective", don't apply. However, "you might be overthinking the emotional implications of the star rating system", IMO, does. Not that 1 or 5 star ratings can't be emotionally impactful to any given buyer, they certainly are.
I'm still sticking to my story that 1 star equals 20/100, and 3.5 stars equals 70/100, which equals a "C" in most scholastic environments.
PS, I didn't proofread this perhaps as well as I should have. Now it's time to dust off that intuition to figure out what I was trying to say.