First of all, FVM is absolutely movement control/debuff of enemies. And if it doesn't "quite" do the same thing as ZB I think that the role they play in a fight are close enough to be functionally indistinguishable.Yeah it's different. ZB is movement control/debuff of enemies and movement gain/buff of allies. FVM doesn't quite do that, and while TRF helps with the defensive aspects it doesn't for the offensive aspects of the buffs.
Second, sure, you can distinguish between defensive AoE buffs and offensive ones, but I think in practice we'd use them interchangibly. While there is certainly some value in being able to choose between boosting our allies' defenses and their offenses, I think said value is minimal; instead of developing that sort of versatility we would be far better off focusing on strengthening one or the other.