Given the tremendous budgets of these games, I don't think a small team of dedicated writers should be out of the question at all. I don't think constant story updates are a problem. But to make the entire process of leveling follow that process would still be unrealistic. Some degree of progression needs to be gameplay-oriented, otherwise your story efforts will suffer.
Ok, now we're going to get slash fiction of Wint x Kachi somehere... rule 34 and all...
Never confuse your inference as the listener for an implication of the speaker.
Good games are subjective like good food is subjective. You're not going to seriously tell me that there's not a psychological basis for why pizza is great and lutefisk is revolting. The thing about subjectivity is that, as subjects go, humans actually have a great deal in common.