It didn’t use to, and would even apply the damage but keep you in stealth. Though I suppose for PvP clarity sake this is why it now removes you from stealth. However, I feel like it should only remove you from stealth if you deal damage with it so you can activate it pre-pull instead of having to go BF -> Stealth -> Ambush.
This is a misconception. Vial was nerfed more than likely because Blizzard thinks Rogue has too high sustain in PvP as a melee class. Sustain in raids will still be high due to Recuperator Conduit.
In regards to Pick Pocket mechanic, that was probably scrapped due to it not hitting the mark for the “feel” they wanted out of it.