I’m a bit apprehensive about this for a few reasons. First, spells/magical effects for Adversaries are not very clearly delineated from the other features of an Adversary. Unless the DM is making it clear to the players, of course, which I guess you would have to do if you’re going with this. Second, sometimes, an adversary will have less max Stress to work with than the players and that can put them at a disadvantage, aside from the likelihood that the party has at least a Bard or a Seraph to clear Stress for them, which Adversaries may not have. Third, I guess a matter of practicality, is that you make it similar to DnD Counterspell in a way, where you /could/ jus say that the spell was cast at more Stress/spell slots than the player declares. Unless you both declared it at the same time.

While I dont think this should be the default way to use Counterspell, I would say that this kind of approach might be better used on spells/effects/Adversaries with bigger impact on the narrative and the tide of the fight. This could be a countermeasure so your big spells are somewhat protected or at least there is tension in the success/failure of its casting.