I would find it unpleasant to be called "C-class talent," but I'd also find it unpleasant to get a C. In both cases, that would prompt me to either step up my game or reconsider my priorities.

People are unequal, and in a business context, that means some people are worth less than others. You can grade them on a curve, but that just means we'll all learn that a "B" means you're a failure, and that really good companies are only recruiting among As and A+s. Differences in ability can't be fixed through semantics.