Vast majority of the complaints, are basically on the wvw domain, as such I will only focus on that (as well as where my experience comes from), in pve, I believe it does take quite a bit of effort, but it’s very much playable in pve, I’m fairly inexperienced in spvp, so my comments do no apply to that.
Toughness
Toughness needs to scale better, having toughness doesn’t seem to mitigate much of the damage from burst builds
Culling
Culling will always be an issue, I don’t think many understand that it’s not exactly that easy to optimize and better culling than massive lag fests. However if toughness scales better, BS thieves won’t be an issue (or unfair) to non-gc builds, so culling really won’t matter here for BS thieves, but still gives an advantage to p/d thieves (refer to stealth mechanic for a possible solution).
Stealth mechanic
Because of that I don’t believe channeled abilities should not lose focus on stealth (status quo), and a a form of diminishing returns to stealth (I would suggest a stackable debuff that lasts 4 secs (maybe even 5 secs) that reduces stealth by 0.5 secs for each stack).
If a thief then uses stealth approximately every 3 secs, the thief would lose the ability to stealth effectively after 6-8 times, with each application of stealth giving less and less stealth duration (to avoid the debuff, they would need to stay visible longer after each application of stealth and of course 0.5 secs is just a rough estimation of effectiveness and balance which can be tweaked appropriately, however I would strongly be against a longer debuff diminishing returns timer as playability in PVE would suffer drastically on certain abilties)
Please note this is an entirely new debuff that can work with the existing revealed debuff that prevents stealth.
Damage
With some of the changes above (please note, I understand toughness scaling may be a huge proposition, but a slight increase in its effectiveness in my limited knowledge may not be game-breaking), I don’t believe thief damage (or multiple ability spike damage) needs to be nerfed as it will only be as effective on other GCs (it’s also one of the reasons why thieves target other thieves frequently, and no, I don’t think other GCs deserve better survivability against another GC).
The spike damage will be wholly reduced on those that have a tougher build, and negligible for those who opt to go for a GC build (the scaling may be universal so existing toughness on GC builds will also benefit slightly).
Final Comments
Please note, I’m mostly in wvw, and my comments come from my experience in that part of play. I play both a thief and a ranger in wvw and while recently I’ve been seeing a lot more folks starting to effectively learn how to counter bs thieves, I still do honestly believe even an unprepared player should atleast have a couple of seconds (extra seconds outside the initial burst) if they at the least built for toughness to make a decision or reaction time.
At this point, I’ve caught unprepared players and finished them in a matter of seconds before they were clue-ed in, and I do sincerely believe, that is not fair and satisfying for both sides.