The balance problem with the thief, is that there is no counter play to stealth. There is only ONE (!) skill, Ranger's Sick 'Em, that if timed properly, can counter stealthing. We need more skills/traits to apply Reveal or other ways to deny the opponent to stealth whenever he wants.
As for the necro, it was overbuffed with all that condition damage, duration and fast reapply. At first the necro was really squishy and it didn't had any survivability, nor damage output, not even condicontrol. Now it have all of them, with condi being the worse.
The overall balance problem is the fact, that Anet have no idea what they are doing.
Firstly, they want to balance the same skills on 3 completely different game types - PvE, WvW and PvP. Splitting the skills' core functionality for every game type will not feel good among anyone, who is constantly jumping with the same profession from PvE to PvP to WvW. But what's the problem in adjusting the numbers(be it raw damage, boon/condi durations, etc) in said skills?
And secondly, Anet's "Balance Team" biggest flaw is that they do not consider previous balance changes, when they make new. That is huge, yet overlooked. That way they are locking out whole professions (not just certain builds) out of content. For example -
the warrior in sPvP, from the latest beta to early after the release, Warriors in sPvP were beasts (mostly the bull's charge hundred blades), while the Elementalists were so squishy, without any survivability or damage.
Then they nerfed a bit warriors, and uped ele's survivability through the water trait line, which also gave them good sustained damage and perma fury and with some adjustments to the other professions rendered warriors completely useless in sPvP for good 8 months(!). While ele was godlike - really hard to kill, with great mobility and good damage.
Then, they start to nerf ele's mobility and survivability(by reducing healing and boon duration), and also giving other professions other ways to deal with certain setups (like thief's larcenous strike, or warrior's destruction of the empowered). Now ele's completly useless in sPvP, because it cannot survive the constant condi pressure, and do not have the damage output to get past the passive healing.
Same thing happened to engies and mesmers, or happening now to necros and rangers. Rangers, for example had really great berserker build with shorbow and good bleeding. Then they nerfed it slower crossfire, less critical damage, and on top of that they made retaliation and weakness changes, that completely destroyed rangers. They were useless for good few months, until changes to spirits in summer.
In short - Anet have a specific meta profession, that outshines the others and they are nerfing said meta. But in the same time they make changes to other professions to counter the already nerfed meta spec. This results in constantly having really viable and must have professions, and on the other hand - a profession or two, that are completely useless and you are handicaping yourself (and the team) for bringing along.
