The quality of service is constantly upgraded, hance prevalance of 5 star reviews, if everything is ok, there is no need to lower the score. There is a gratitude.

Which is exactly why a 5 option rating system isn't even appropriate within the context of the given example. Just another way we can see that the rating systems are inherently flawed to the core. For something like a restaurant review it makes way more sense to just have 3 options, as most reviewers are never going to need more precision than that.

This is also something I have talked about at length, and I even came up with a way to make different rating systems compatible with each other using odd-point rankings.. If there are an odd number of options available every ranking can be reduced down to a percentage that meshes will with the other ranking systems. The most common systems being 3-point, 5-point, and 15-point rankings. Where 3 point is pass/neutral/fail, 5 point is 5-stars or A-B-C-D-F, and 15 point is A-B-C-D-F with a +/- option. The maximum option would be 101 point scale where reviews are graded directly with the percentage itself from 0%-100%