UNIT - Creature Balance + Visual Changes

1) If I understand you correctly, you are suggesting swapping the positions of the witches and hydras? The idea is interesting, but in that case, the hydras will turn out to be very durable, even more so than ents (especially the upgraded version with regeneration).

Balance here is a matter of numbers, i.e., everything is changeable. Work with the stats; you can also play around with the regeneration strength if you want. I would do the same in my mod if I hadn't decided to put the faceless ones on tier 6 (meaning I removed the hydras from the Dungeon altogether).
P.S.: I removed the hydras for two reasons:
1) They belong on tier 7, where the dragons are;
2) In Heroes 5, hydras are terrible - a bizarre, unstable, awkward, and ugly unit with a disgusting animation - IMHO.