Yes, there are situations where Defense is more important – these are situations where neutral creatures attack first, assuming, again, that we have a significant advantage. This applies to archers, flyers, and simply fast units. Taking Utopias, for example.
...In my mod, heroes will cost 5000. At the beginning of the game, players won't have many of them, and there won't be chains either; there might not even be much micromanagement, or at least less of it. Closer to the end of the game, chains are needed less, as the main hero's mobility increases (City Portal, etc.), and a large army accumulates, which needs smaller reinforcements, the size of a weekly increase, less often. By the way, the City Portal will be slightly adjusted.
In Heroes 4, the hero system is implemented differently – you can only hire 1 hero per week in any tavern. And you can only pass artifacts along the chain, but not monsters.
Справочник по НоММ-4 http://handbookhmm.ru/pamyatka-dlya-heroes-iv.html
Памятка по НоММ-3 http://handbookhmm.ru/pamyatka-dlya-homm-iii.html
и HotA http://handbookhmm.ru/vyishla-obnovlennaya-pamyatka-dlya-homm-iii-hota.html