Making these abilities group-based would exactly serve that purpose, not prevent it.
That's simply untrue.
Your individual persuasion affects the outcome as much as your tags do, and having a Barbarian borrow a Scholar's or a Noble's Persuasion for the purpose of his brutish grunts is simply ridiculous.
Barter is on the same boat, because your characters build relationships with traders on an individual basis.
It's entirely possible to have your top Barter character have a negative attitude with a trader, while everyone else has a positive one, and making barter global would let you completely bypass it.
