I think you're overemphasizing the confusion that an alternate ranking schema would cause. We have Rotten Tomatoes as a very obvious example of one that a lot of people are perfectly happy with even though it's doing something very different from the usual meaning of X% ratings.
I feel like all that's really needed is a clear indicator that it's some proprietary ranking system (for example, "Tomatometer" branding), plus a plain-language description of what it's doing for people who want to know more.
I feel like all that's really needed is a clear indicator that it's some proprietary ranking system (for example, "Tomatometer" branding), plus a plain-language description of what it's doing for people who want to know more.