Harmony - Troop Symmetry

The tactic of not building up an army, but instead investing in development, isn't very good because at any moment a plague week can happen, and the growth accumulated over a couple of weeks will simply be lost – it's like saying: "Come on, enemy! Take my built-up city, I have no army, and I'm defenseless."

7 days is a long time. Besides, 1-2 units of level 6, and especially level 7, can mean much more than several smaller unit reinforcements (especially considering the advantage of having more than one battle). For example, 2 Paladins can win a battle in which units of levels 1-3 would lose.
And the opponent still has to get there. If the map is bare, then of course. But if not? Rebuilding a city is something that should be done in the first month, not in the middle of the game.
Although, maybe on lower difficulty levels, the hero is... I haven't played on those. There, the neutrals are weaker, right?

Added 2 minutes later

Why prolong the game – I don't understand. The essence of the battle is war, the goal is victory.

Personally, I've heard that "Heroes" is positioned as "tactics," not a brawl. And tactics are not only the final battle (neutrals are not essential), but also actions on the map.