I did a lot of DnD PvP back in edition 3.0. We ran an number of battles where everybody built a silly, twinked out character to see who was the most absurd. I think the final character I settled on was a ludicrous level 8 sorcerer / level 1 paladin who polymorphed into a stone giant. I had truly sickening defenses due to super stacking my charisma and getting a ton of natural armor from being a stone giant and beat down pretty hard too - a trip specialist with stone giant strength is pretty terrifying. In the end though fights still came down to a single round or even a single roll. I made most saves on a 2-3 on a d20 but you could still beat me by just hucking a save or die spell my way and hoping. On the other hand I hit so hard that nearly any character would be killed within 2 rounds of coming within my reach and would spend nearly all that time on the ground.
In the early going of DnD Next I really had high hopes that they would reverse this trend. It looked like they wanted to give starting characters more hitpoints and reduce the reliance on instant death attacks but in the latest iteration that seems to not be the case at all. Right now things are just as lethal as in the good old days. Now it might not be much of a design priority for PvP to be balanced but it seems like that would be quite valuable. NPCs could reasonably be built using the same system the PCs use and the fights would make sense. Enemies could have stat values that were comparable to player stat values and if somebody changes sides combat mechanics would still work.
Some examples from the current DnD Next (I made some reasonable assumptions about stat allocation): Wizards have 6 HP/level. Wizards also have a Magic Missile spell that does 10 damage per two levels, rounded up. This means at level 1 Wizards have a totally normal spell that instantly kills another Wizard without a roll. Fighters swing for 12 damage at level 1 so they also one shot kill other characters but at least they have to roll to hit! This is all nothing new though, low level characters murdered each other instantly in past editions. (That doesn't mean it is a good thing.) The real trouble is characters are now one shotting each other even at high levels, and without using Save Or Die spells. Magic Missile scales up very nicely and is doing 50 damage at level 10 into a Wizard's 70 HP. That isn't a one shot kill, but it sure hurts! Fighters at level 10 are swinging with their two handed swords for about 40 a round into Wizards so death is swift on all fronts. Except rogues, of course, who suck, and Clerics, who desperately try and fail to patch up the heinous wounds being inflicted. Any time a critical hit happens the target simply explodes.
This just isn't right. While I like the idea of character progression I really don't see the need for such extreme differences between the early levels. A level 12 can fight a level 10 but a level 3 has triple the health and does double the damage of a level 1... they aren't even playing the same game. Two major things need to change. First off, people need to do way less damage relative to their HP. Second, the game needs to start off at level 5 or so (by current mechanics) so that levels aren't doubling character power. Level 5 to level 6 is a big boost, a noticeable boost, but you are still playing the same game. Also, fix rogues and let them be decent in a fight. Garbage at fighting and godlike at skills isn't balanced, it is just pigeonholed.