Heroes 5.5 WarGame Edition - Tactical Edition.

I suggest strengthening the creatures as in the mod for higher-tier creatures (it also included an azure dragon instead of an emerald one, and other creatures that were too powerful), but at the same time, make them more expensive and, as you wanted, reduce the growth rate.

At a minimum, you can build a base + upgrade in the second week, and that's already 1+1 = 2 dragons. Currently, the value of 1 dragon is about 6,000 (the same as a Capitol), 2 dragons - 12,000, this is a very strong unit even without strengthening it, just to prevent new dragons from appearing in weeks 3-4.
Besides, don't forget about the very strong Death Chill spell, which will be even more effective against super dragons.

My main criterion is how the game will look in the first month, especially in weeks 1-3. Supporting a mega late game for more than 1 month is good, but only if it doesn't affect the early stages. The number of dragons in such a late game will be at least half as many as in the original, due to +1 growth instead of +2. And that's already good.

So the game will last for about two months. Okay.

Where did you get that conclusion? I said that it will be possible to build a Tier 7 unit at the end of the first or beginning of the second week, which means it will also be possible to upgrade the guild to level 5 in the beginning of the second week (although it will be difficult).

Didn't you increase the experience required for leveling up?

It's hard to say, but in any case, the goal will be to gain +1 level per day (slower at levels above 10-12).