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Shifting the berserk to a buff essentially duplicates the Light's Righteous Strike in the Dark faction. For this reason, I decided against such an implementation.
Our idea behind building the new berserk is actually what the whole new magic system is based on. Every school has a strong side and, to some extent, can cover a little bit of the others.
Summoning is based on summons but can also add some durability and some damage - raise dead (level 2) and shield (level 5), firewall (level 4).
Light focuses on durability spells but has some direct damage + crowd control - vengeance and word of light, teleport.
Dark focuses on crowd control and weakening but can also do some moderate damage + endurance - vampirism (level 5), world of the netherworld (level 4), decay (level 2), the new Berserk (tier 3).
Destruction - Besides the heavy damage, it also adds some minor weakening and crowd control effects - fire/ice/lighting perks, Deep Freeze effect.
Note: All spell levels refer to the 5.5 mod. "Minor" or "moderate" refer to the spell effect of a spell compared to a similar one from a school that leads in that aspect. For example:
When talking about moderate damage in the Summoning school, let's take the Firewall spell (level 4) as an example. I compare it to destruction spells from level 4.
Some values to compare with:
Destruction:
Meteor Shower (level 4): 20 + 20*Spellpower damage, 4x4 area of effect.
Chain lightning (level 4): 32 + 32*Spellpower initial damage (60 + 60 all 4 hops damage).
Summoning:
Firewall - (level 4): 20 + 20*Spellpower damage. 1x3 area of effect.
Comparing them, it's actually the same damage, but the firewall is harder to cast due to lower range.
If we do a similar comparison for crowd control spells in the Dark school, it's obvious (having in mind the previous comments in the thread about pros and cons) that it is a much better spell than any of the level 5s from other schools.
With the new approach, Berserk is a tier 3 spell with a significant damage boost but low tactical benefit (you lose control of your unit, and it will probably be exposed for a number of hits from the enemy factions). Here is a comparison with Righteous Might and a hero with 20 spellpower.
Expert berserk damage base + 150% + 1%*SP = 150 + 20 = 170% bonus damage for 1 round (I am disregarding the bug we can't fix).
Righteous Might - (8 + 0.15*SP)*3.33% = (8 + 3)*3.33% = 11*3.33% = 36.63% bonus damage for 2 + 0.1*SP rounds = 2 + 2 = 4 rounds.
So, a unit with berserk will do 170% bonus damage, and a unit with Righteous Might will get 36.63%*4 = 146% bonus damage, but the berserk unit will suffer the penalty of being caught off guard.
I cannot prove to you that the strategic penalty is worth a 24% damage increase, as we came to the conclusion that any change is worthy if we see that it is not abused by players (overpowered) nor disregarded by them (useless).
In order to get rid of the personal bias factor, both players always play the final PvP battle from both sides of the battlefield. The stronger your hero is, the harder you will be punished 50% of the games. So, in the end, both sides feel the bitter taste of their own strategy, and eventually, players make a mutual decision on what strategy/skill/spell is strong or weak or just as good as it should be.

