What truly needs to be nerfed is the Longspear/shortspear proc for defense pen.
Here's the true issue:
First, when combined with puncture (which procs often), darkrunners can nullify 12k physical defense with ease. Unless you're in high end plate or leather, that is more than most people have period.
Then, when you stack things like the 2h buff for 50% shield pen, they go even higher than that.
Combined with other things like normal defense pen from weapons and accessories, it goes even higher.
All told, darkrunners can nullify around 15-20k physical defense without much problem. Bye bye tanks.
Combined with bullshit like attack and retaliate, and the absolutely insane damage of instant skills like BEL and Precision strike, and the backstab damage of things like Shadow Smite, you end up with a situation where all a darkrunner really needs to do is trip, and suddenly someone is getting face rolled. Most of the time, darkrunners don't even need to trip, they just need the passive to proc, and suddenly their front facing precision strike on a target that isn't bleeding, has a shield and 9k pdef hits for 11k (I've had it happen to me more than once).
It isn't just Darkrunners though. Combined with the above passives, most classes that leverage battlerage have these advantages. Dervish, Argent and Abolisher are some classes that come to mind. Tanky AND powerful. Kind of bullshit.
In addition, it should be noted that because CryEngine is shittastic crap, you have another all together fucked situation, where melee has the advantage of lag. In essence, when dealing with a melee, on your screen, you can be tripped nearly instantly, due to the latency involved with recalculation of player movement, and skills that are cast. It is extremely common to be instantly tripped after being hit with Overwhelm > Shadowsmite, or even more commonly, BEL and Triple slash. On your screen, you're flat on your back or face in an instant. And lets not pretend that macro-runners aren't a thing. Nearly every darkrunner is an entitled little shit stain that picks the class because it is the cheesiest of cheese, and they scream murder when they lose.
And lets not even mention how busted up the arena is. I feel like it was coded on P2P networking, with how laggy it is. You can straight up nail people with AOEs and attacks, and they can just outright ignore them or teleport away a full 2 seconds later, entirely unharmed. Some real shit there.
On the other hand, mages have the staff proc that can ignore 10k mag def, and combined with weapons and accessories, they might be able to hit 12-14k mag def pen, if they're lucky.
Leather has zero issues reaching this kind of defensive level, and forget about killing cloth clad healers at that rate. They additionally have high cast times and combination setups that they must contend with. While all melee users need to do is stack a little bit of attack speed, mages have to stack attack speed AND cast time reduction in order to be fully dangerous. Even when mages do this, they STILL require planning and skillful deployment of skills, unless they're carrying around high end epics or legendary weapons. Combine the above the fact that mages have no additional defensive penetration OR skill resets from their skill trees, and you've created a highly unbalanced situation.