The most useful spell.

I meant a parameter like initiative. After all, a game with clear rounds (turns) is played like chess. There are many guides on clearing utopias, crypts, and so on for the third game. Because it is clearly understood who goes and how, the game is about waiting, and so on. You can't do that with initiative; battles with it are more... random, perhaps? Because if you remove the ATB scale, it will be completely unclear who goes after whom. It's unlikely that this is suitable for esports, where randomness was removed with tons of rules. But for PvE gaming in the evening, "for relaxation," with thousands of creatures, I think the fifth game is the best.

I strongly disagree here; in my opinion, ATB battles are the best thing that has ever been in the world of Heroes, especially in terms of interest in PvP and the richness of tactics.
Yes, they are more difficult to calculate than linear rounds, but that's what makes them so appealing.
The randomness of the scale is actually quite low and only manifests itself when the initiative of a particular unit changes or during a partial turn (waiting, mass cast, spellcasting).
Also, there is randomness in the starting ATB, as Ment wrote; in my opinion, the random spread is too large (25%), so it appears not only with equal initiatives. But this is not a problem of the scale itself, but of the initial spread.