Heroes 5.5 WarGame Edition - Tactical Edition.

Compatibility with Eternal is planned for when the project reaches the appropriate stage (i.e., when there are games on the map, not just duels).

In any case, as I already wrote, especially on large maps, playability will be present even WITHOUT active AI resistance, simply because the player (on a high difficulty) will be competing with neutral creatures. Every week on such a difficulty, the number of neutral creatures will double, which means that if the player plays slowly and not efficiently enough, they will lose (be unable to win) simply because they won't be able to defeat the necessary neutral creatures in time. Since they will not be able to double the power of their army every week, over time, the relative growth rate and strength of their army will slow down significantly. And they will be forced to break through as quickly and efficiently as possible, capture cities early, hire additional heroes and new troops, etc., in order to complete objectives before they become impossible. Thus, for a competitive (sporting) element, AI is not necessary. It will be possible to play maps without any active AI participation at all.

For duels, everything is fine, of course. But this won't work in offline mode. Rapid development and timed capture of mines, key points, etc., is not very good. Such development implies perfect knowledge of the map, race, vast experience in Heroes, and knowledge of all units, races, and classes of this mod, etc. In general, all newcomers, those who like to play slowly and defensively, and other players simply won't be able to play. It seems to me that this forced acceleration is unnecessary, at least for offline play with AI. It is better to play based on the number/quality/prices of buildings and recruitment/certain tactical moments and features of each race - this will provide extremely flexible gameplay with a huge number of diverse tactics without artificial stimulation from external factors, and leave the pace of development and other nuances to the player's choice.
That is, I understand that we are talking about a hardcore difficulty, and it is possible to set the difficulty to medium so that it is not so harsh with the neutral creatures. But as I understand it, the AI level will also decrease. As a result, it will be uninteresting to play on medium, and impossible on hard.