What would you change in Heroes of Might and Magic IV?

It depends on what you consider to be similar... After all, the first one simply attacks in an area, while the second one does so with some caveats.

Yeah, they attack the enemy with a sphere. And the ring affects your own unit when it's surrounded :) In theory, the effect is similar. But Chaos needs a large amount of magic for damage, even if it's slightly different, to increase the probability of it appearing on a floor.