I believe you grouping is good...
Free Characters, Base Set Characters, and the Expansion pack.
My belief is that, with the season pass, we will have access to all three groups. I also agree that access to the character expansion will not change my decision about my investment to the game. I will be purchasting the season pass.
If for no other reason to support the game.
My favorite characters is Amiri. I love the Barbarian.. She is absoluely a beast.
If I am forced to work with out her, I will be adding her as soon as I can. I have to believe that the season pass cones with the entire base set characters..