Good Tanker units?

[Vilk]

1: I agree initiative is a burden but for a tank it's a less major burden. You can manage that and if you use target you don't care much of the initiative for your tank.

2: It seems you never used Ancient Ent so don't even start to suspect how strong they are. Ancient Ent moves of 1.

3: Same than above, use them before talking about them.

4: You didn't read the Divine Armor trick, it cancel fully the fire penalty and add the full resistance from Divine Armor.

5: Easy.
With mage learn Higher Magic.
With Paladin and Warrior learn tactic level 2. Put Ancient Ent as far than possible from your side. Cast Target on it, long range are already busy with it and won't hurt your other troops. Other enemy troops won't reach you in round 1 or Dragon and Archdemon won't care of your target and tank anyway. Round 2 teleport Ancient Ent at the best tank place.
I agree that slow tanks are more for the mage.

Overall, my comment about Ancient Ent is more for a mage but that need more testing with a warrior. Also I have to admit than if I use them including a little as tank, I haven't yet tried with the Divine Armor trick that change a lot the point of view.

I also agree with you that mobility is an important factor for a Tank. About using only Horsemen as tank through all game I'd say that tank is a major role and use one or even two reserve slots for more tank options is a more efficient approach.