If these are the most problematic I think we will be fine.
A reasonable view and I agree with you, if we look at rogues, specifically at Assa in isolation. With this pov Assa was fine in BfA, in SL, in DF and will be in TWW. There are quite a few other specs though which have, to use a car analogy, more direct steering, better handling/gearbox/transmission, more torque…for the same price tag.
Deathstalker’s mark being applied with ambush is making a big deal out of one GCD. You’ll use it once per pack and get re-applications (if stuff lives that long) on finishers. Target the prio kill target and viola. It’s not that rough.
Well beta m+ tests have shown that quite many situations during a run come up where you re-apply the mark at a dying mob/pack (e.g. lost 5-7 sec), go in to your opener rotation for the new pack and if timings go wrong you can’t get the capstone in time. So in order to get the capstone you need to alter the optimal opener rotation just to not lose out on the capstone effect.
And I’m not even talking about first boss in Tirna Scithe where you mark the tree which goes immune in intermission and your mark/capstone is being lost. Same with Last boss in necrotic wake when it selects you being sent down.
In essence, the whole mark/capstone design is flawed not taking existing boss mechanics and m+ pack design into account.
It can be argued, if Ambush is the right skill for applying the mark. I think it is problematic as you don’t have many possibilities to access it. Shadow Dance is gone, 2nd Vanish is not being played as pre-requisites Subterfuge is a dead 2-pointer and Soothing Darkness is outright bad for Assa. Three wasted points.
Blindside is an option but unreliable as you don’t know when the proc happens and if you play Bone Spike/bleed build you don’t have Blindside at all.
Singular Focus? - Correct. It is a bug that needs fixing.
Let’s hope so. It is currently not acknowledged as a bug by Blizzard.
Lingering Darkness? Yes, it’s not great. But it’s really not what I’d call a “major problem.” It’s boring. It could be better. The end.
Correct. What does it tell you about the design intent of the dev team, though? “Hey let’s bring back a universally disliked and bad tier-set effect bad instead of designing something worthwhile”.
Your final point, while valid, seems to be a bit of a slippery slope fallacy of “where will it end?!” Until we are at the point of using aoe builders in single target, I don’t think some scenarios where there is overlap is a dire problem.
Last tuning pass from July 31st brought FoK now firmly into ST territory. Before last tuning pass it was “just” a possibility.
My take is that boring, completely passive Fatebound looks more and more appealing than Deathstalker. Current numbers show it within 1% ST dmg margin and already way ahead in m+.