As for you calculations:
Hmm... the bonus doesn't seem to be multiplicative to me but additive. +30% from STR and +30% from 2H for example result in the same damage as +60% from STR alone.
And even then, going first means having always n+1 rounds of combat. So in the worst case it's all or nothing, but even in round 2 it's still worth +100% damage, +50% potential damage in round 3, and so on...
Going first doesn't help much with melee char if they can't get in range. This is why I never want my powerhouse to have high wits because even if they can move, unless characters like Lohse spends time repositioning everything just to get them into the 2H Red Prince range, it's a waste of AP for the 100-0 Rage combo. By learning how the AI works, it's way more effective to wait for their melee to get close to you (abusing their wits) and then reposition the range into that melee to have more targets in a world of hurt.
And it's actually multiplicative.
Warfare: The bonus is weird and will require some explanation how it really works. This talent is based off the final damage of what you do and scale with crits as well. This is multiplicative. It will grant you bonus as long as your initial hit does not break the enemy armor and the bonus will never be high enough to hit the enemy health directly.
Let's say you deal 50 damage and have level 4 warfare (+40%). If your enemy has a lot of armor, you will deal 70 damage on that hit, dealing 50 first followed by another line of 20 from Warfare for a total of 70. If you crit for 100 damage, that extra damage becomes 40 for a total of 140 physical armor damage.
However, take note that the 2nd line of damage WILL NOT appear if you break the armor or the bonus breaks the armor.
If your opponent has 75 armor and you deal 50 + 20, it will show 50 and 20 from hitting, two seperate lines of damage.
If you deal something like 60 + 24, it will only show up as 60 yet still destroy the enemy armor (warfare bonus damage line does not show in this case and it is bumped up to 7)
And if you use the crit number of 100 damage, warfare bonus will not be active at all because you already destroy the armor.
Easiest target to check this is either hitting your shield teammate or Zaleskar if you want to use abilities to confirm this.
2H Talent : 2H offers both weapon damage bonus and crit bonus. Kinda easy to tell it's multiplicative already just because of the crit bonus, further strengtening how strong your initial blow already is from getting tons of crit.
Elf Racial : +20% damage is multiplicative.
2x Snipe and high ground Bonus: Multiplicative.
So when you build that power house char, you have to consider how strong the bonus becomes as you level up. When you have like 10 points in 2H, the crit bonus jumps from a base of 1.5x to 2.0x or even higher if you have at least 1 point in scourge for adrenaline/walk-in-shadow. Simply getting 2 damage per Str might seem low now but just looking at a 2x crit bonus, that's a 4 damage loss per point when Rage is on. When you hit 3x in a single turn (Crip, Whirl, Battering), that's 12 damage loss
per level.
If your character has to take 2 turns to kill something compaed to only 1 turn, you are already losing the AP efficiency factor especially considering how buffs current work like RAge not really disappearing right away after you get to play your turn again and you can still use it one more time. Also, skills have cool down so even if you act alot, you can only normal attack.
With multiplicative factor in skills like Criplling, One single super strong str-build blow will end up dealing enough to efficienly kill targets compared to 1 crippling + 1 attack from the Str-Wit build. When you add in the AoE, you can see how high the number goes up especially if you take Warlord instead of The Pawn.