You have to take into consideration PK ranges. A level 50 Elf Paladin reaching down to fight a level 42 human dark-knight. Or a level 50 Drow Shaman reaching down to fight a level 42 Ogre Warrior.
How is a drow shaman at 50 beating on a 42 ogre warrior any different from a human shaman doing the same? I guess that's my basic question.
If it's a basic stance of a level 50 paladin, or any class, beating on lower level players easier than any other class, just limit their ranges based on that fact alone. Have a pk range guided by class alone?
The number one reason I don't play Elves, blademasters, paladins, etc. is because of xp pen. But that's just my reasoning, and it's certinly not the reasoning for many other players. And, in all honesty, the current system isn't broke. So why fix it? But as for berserkers's pen.:
It's kinda a rough and tumble road there. As they have a massive powerspike at the lower levels that is rounded out by the exp pen, but as they get higher it severly limits them. At least that's my understanding from the posts I've read (haven't pinn a zerk). I suppose you could look at it by way of at the lower levels the xp difference between classes isn't much, so a one or two level increase in their range isn't that big of a deal.
And there are many inncentives for moving up the ranks and not just sitting still. As it stands, there is only two reasons to sit at the lower ranks: Training and waiting on a quest app. There are systems in place to prevent people from sitting at one level and just going on a killing spree... I've seen it with my own two eyes, and an immortal doesn't need to be on for it to be present and active.
So, I guess my point is: I really don't understand why the Berserker has a 250 xp pen. Hrm. Could have summed all that up in a lot less words, but would that be my style? 
a-g