Am I right to think that quests like Waitress, Blacksmith and so on doesn't increase stats? Slave guild quests should increase Charisma. Wizard Guild Wits, Warrior Guild Strength, Worker Guild either Wits or Strength depending of the quest.

As a side note there's no way to increase Charisma anymore except Charm training during a date since Social skills have disappeared. Maybe slave training could increase Charisma.

Regarding the side note: If you're talking about the Charm stat and not Charm Factor, characters can increase those through persuasion events where one has to expend a Persuasion Charge or when selected to negotiate the recruitment of a character found in the dungeons. Service tasks for waitress and stripper also still build charm.

As for the main point: I have not noticed stat increases for characters assigned to job-quests, but I was not looking for any such changes. A small experiment in my current game leads me to agree with your assessment since advancing 15 turns and monitoring the assigned characters showed no growth of the requisite stats. That is not definitive, since those characters have bad factors, but it would seem doubtful that all three characters would not see a single point of improvement if job quests did still count for stat increases.