As Chameleon once aptly noted: “A spell that can be dispelled has no place on the fifth level” ©. Otherwise, it turns out that the second level can negate the fifth. The Mirror of Pain, in addition to being dispellable, is also quite useless in itself, because in the game, troops are usually not lost, that is, our troops almost do not take damage. And if we are talking about the final stage, then no one ever kills troops there; the main targets are heroes, and if the heroes are defeated, then what spells the troops have is not so important.

Chaos has simply weak Armageddon and Haste on the fifth level. And in general, 4 skills in resistance completely negate the fifth level of Chaos.

Not even the second, but the first. Yes, I agree that the Mirror is not so relevant in the final stage, but Hypnosis and stealing all the spells are very relevant in the final stage. And if we reason like that, then almost all spells can be dispelled or canceled with Counterspell or Dispel, but firstly, you still need to have time to do this (for example, before the hypnotized creature/hero attacks), and secondly, it is clear that the main hero will not do this, and the secondary hero may not even survive. So, it's not that simple. By the way, if the Angel in Equilibris is moved to the third level, then what remains on the fifth? Sinking and Divine Intervention?
Resistance certainly negates it, but not all heroes will have resistance, not to mention creatures. Armageddon is not relevant because it affects allies, but Haste and especially Disarm can be very useful.