I think the sort of complaint about review scores seen here is the result of people who aren't actually looking for recommendations for games when they see reviews, but are actively seeking out validation or points of contention for views they already have. I think the prevalence of pre-ordering reinforced that dynamic.
Regarding the title assertion: So you'll ask them politely? All of them? A review is editorial. It's not binding, as far as the end-user is concerned. I don't think you've made a compelling case for why numbered reviews "must" stop. People and outlets choose the forms they do because it's made sense for them. It's quite bold to say, in effect, you know better than their collective reasoning on formatting. I don't see how end-users are harmed by the practice, and it hasn't been explained here.
Regarding your primary question of how you can quantify a subjective work: This is a necessary process (imperfect or otherwise) to help curate any creative work. People seek these reactions out. The numbered review is a distillation of the recommendations of the reviewer. Full stop. It's no worse than pulling a selected blurb of a review. I think numbered reviews exist for a reason. That being the amount of energy it takes to read and react to dozens of write-ups for every game release. I say this as someone who goes out of his way to read long-form reviews.
I don't understand the imperative to stop quantifying the reaction to games. The written reviews are the core of the commentary. Numbered/lettered evaluations are a layer above that. They only have as much value as you ascribe them. Honestly, most people I see aren't looking to reviews for purchase recommendations. They're looking for a way to justify or react to viewpoints they've already made. If you honestly feel helpless in terms of knowing the quality of games in this day and age, there are plenty of ways to find this information. Streaming, Youtube, write-ups, discussion from users. Waiting, if you're actually concerned about the quality of a game, is a very simple thing.