Lone Wolf is exceptionally strong on Hard because of the way difficulty scaling is handled by the game. -25% Vitality (Hard) +80% Vitality (Lone Wolf) means a net +55% Vitality, which is more than double the Vitality of -25%.
Your math is horrible. It's only a 35% increase. You don't subtract 25 from 80 to come up with the number. You subtract the 25% from your base, then add the 80% back (or add the 80% to your base, then subtract 25%, not sure which). Either way, it would look like this, using 100 as the base vitality for an example:
100 - 25% = 75
75 + 80% = 135
alternatively
100 + 80% = 180
180 - 25% = 135
Either way, net result is the same, only 35% increase. Obviously, higher numbers will make the two formulas differ slightly (since you're reducing from the 80% as well, if it's the latter formula); but it's not a 55% increase in any event.
