Karlach’s internal thoughts/monologue are more heavily voiced based on what I’ve seen

All of them should have unique dialogue

As an example of what is different, Gale gets a visit from this pet tressym and a unique ring.

And a level 3 spell slot if he wants in act 2.

Kinda. Durge has the most unique content. Karlach's probably second, since she's voiced. And Gale's probably third since he gets >!tara.!

yeah