I would first like to say that the stealth revamp and the vision cone in deadfire is miles ahead of what we had in PoE1. The system helps a lot in making rogues and sneaking more immersive, and backstabbing is an actual thing now unlike in the previous game where it was basically an afterthought.
That said, I think rogues here have another problem - too many similar skills.
Hobbling strike, Blinding strike, Strike the Bell, Finishing Blow, Withering Blow, Sap, Gambit and Vanishing Strike. That's 8 attack abilities not counting the various upgrades for most of them. I'm pretty sure most players don't need them, and some are pretty much wasted space by the time you get to them (why would you ever use sap).
You might say how it gives rogues options, but not really, most of these work pretty much the same and are boring in effect, with the exception of finishing blow and vanishing strike. Gambit single-handedly trivializes any kind of choice once you unlock it. But if you nerf gambit then you're just forced to use a combination of the other strikes.
If you ask me, we should drastically reduce the damage of some of the strikes (strike the bell, sap, withering blow for example) give them some sort of utilitary role, or replace them completely. Sap could stun the target but do 10% damage. Put in rogue-specific poisons that are more effective, cheap or can be used per-encounter like poison that lowers stats, armor, defenses or fighting capabilities of stricken targets. Put in skills that promote gun/sword combos. For example a Ranged or Melee attack that does not have recovery as long as you used the opposite weapon before it.
I'm pretty sure I'm late to the party when it comes to these suggestions, but maybe for a bigger patch or expansion there's hope.