To talk a little about unholy melee and why it's no bueno to have vitality also increase damage:
In general in fighting games there are three types of classes:
-Tank / brawler
-Glass cannon
-Well-rounded, not the best at anything, but not the worst either
None of these things is an issue unless if the game environment is making it easier for one of these to navigate trough than the others. There are clear advantages and disadvantages to playing one or the other. Now what was done with UHM sort of breaks these archetypes, and combines the best of two worlds into one: the glass cannon and the tank.
Unholy melee was a shitshow before, I think most people could agree to that, they usually just ran in and died before getting too much damage in. But this step is a bit drastic and throws it all the way to the other side of the spectrum. Everyone can see why having a singular stat (vitality) that increases both your toughness and your damage will make a class that's going to be conceptually overpowered. We see this in other games as well, (for example DotA or Heroes of Newerth) where balancing those kind of classes/heroes is a nightmare.
Alternatives to doing this:
-Have unholy melee spend HP instead of mana to deal damage
-Along with the above: create a "the lower you go" mechanic, for each % of HP missing, the unholy paladin gains damage as well as damage mitigation of some sort (resistance / armor / whatever)
-Below is based off the idea that damage scales off any stat other than vitality
- Give unholy melee a shield buff based on the damage they deal, passively the shield regenerates to 33% of maximum capacity. It might feel like this creates another immortal class, but shield generation could be capped at a maximum rate, and the regeneration can be toned up or down based on current level, or just across the board to keep it in check
-The simplest: reduce the amount of HP unholy melee gains trough vitality, though that would fuck with the early game of the class
-Give unholy melee damage mitigation based on the enemies in a certain radius, elites and bosses trigger a higher shield so that boss fights don't make you feel like paper
Anyway there are more ways than this to do something about it, but in the current state, it's just stupid strong by having it both ways. I say all this as a paladin player, my first playtrough was as unholy melee, and I love seeing it strong, but this is just no bueno design.