One could argue that 25% dam redux isn't overpowered...unless you can stack it 8 times. Volkov is probably rocking the following:

barrier - 50%
aura - 20%
shield - 20%
5 invoker shields - 33% (possibly more- but 33% for the sake of argument)
protection - 25%
stoneskin - 25%
stoneform - 25%

So his damage taken is 0.50 * 0.8 * 0.8 * 0.66 * 0.75 * 0.75 * 0.75 = ~0.09.

He's taking 9% what he would sans protections, meaning it's the equivalent of him having 11x his normal HP.

If the fort guys only have mantle then they're taking 75% normal damage. If they all have the same base hp, then Volkov's dam redux means his "effective hp" is equivalent to the "effective hp" of 8 forties with mantle. But remember three of the ones in this log are vuln_drown, meaning that with only mantle they're actually <i>worse</i> off than an unprotected human. Also he can do area damage, multiplying his damage output by the number of people in the room (more or less).