Well, judging by my old-school friends...
I'm not quite talking about that. I'm talking about the loss of dynamism in these battles. Previously, any mistake had its consequences (limited resurrection), and the damage of the units was much higher. As a result, the battles were faster.
But 6HoMM is built on the principle of "drag out the battle as long as possible" – medics, strong healing magic, incredibly powerful mass vampirism, tough units.
Ima, 2D 3x is the best.
Consider, for example, the human units: a paladin in shining armor with a spear (SLA), a paladin SLA with a crossbow, a nun (wow, not a paladin SLA, a breakthrough!), a paladin on a shining white horse SLA, a shining golden thing (it's great to create a unit in a prequel that doesn't appear in the 5th part, don't you think? Although maybe they died on the way to the 5th part, who knows), then – a paladin SLA with wings, called an angel. It's great when a tier 1 unit looks like a tier 3 unit, and all the other units are clones of each other, don't you think?
X3, I played Civ normally.
But again – there weren't such terrible bugs as in HoMM6.
And your "it's always been like that" surprises me. Do you really enjoy playing such a raw product?
You're talking directly – healing (and buffs/debuffs/disables). And it determines the battles, killing the dynamics.
P.S. I'm curious why the developers, in the process of simplifying the game, didn't go all the way and leave only one resource – gold and one unit with the same parameters but different models (as in Warcraft 2). What, it's quite logical. And you don't have to think about balance.
Added 2 minutes ago
There are no worse or better parts in Heroes. Each one is better in some ways and worse in others. Official statement from an old-school player.