I somehow managed to complete that map section with the dragons quite easily, it took me about 40 minutes in total. I spent half the time gathering morale in the last garrison, and even had to return for the +3 morale bonus. The order in which the last stack of surviving dragons attacks is also important; it should target a single unit in the second round. Perhaps the difference in the number of troops is a factor. As far as I remember, there were single units lost in all the garrisons. The most I lost was 5 halberdiers against the Azure Dragons (yes, they were divided into 5 stacks). I think losing over a hundred Imps is acceptable, but losing that many halberdiers is undesirable. I'll try to provide a more detailed explanation (with a video) later this evening.
Is the Heretic with Crystal magic the hero who also has Cyclops in his army? If so, you need to take an Ifrit and a stack of peasants or Imps with you, in a number sufficient for the first cast of "Companion" to be "Fireball" on them and the catapult. We, in turn, cast "Forgetfulness" and support the gate with the Ifrit. Then, "Armageddon."
The Red Heretic is very strange; he didn't want to cast any spells except Slow for a long time. In the end, I had to take 30 Imps instead of peasants, and then he realized that Imps are evil and need to be burned xD Thanks for the tips. I guess this map is too difficult for me, since so many details need to be explained =))
The lack of a decent growth rate has a significant impact; every battle is a nightmare.