Options
How much better would it have been if thronebreaker required abyss completion instead of r3 6*?

I'd say 100000% better. Progression should really depend on how far you are in content.
8
Comments
Because the story arc content is itself content I would expect the average player to eventually be able to get through, it can't be excessively difficult. And because there are caps on how difficult it can get, there are limits to how high a progression title it can gate. You can't make a progression title intended for the highest, strongest players in the game and make the content gate something average players can knock off six months after it is released.
So if you want progression to be determined *only* by content progress, you can't make end game targeted progression titles. Top tier players just have to wait until the average players catch up to them before they are allowed to progress higher. Conversely if you make a top tier player progression tier gated to game content, it either means the bulk of players get shut out of the core content of the game, or so-called optional content becomes non-optional if you want to progress in the game.
So given those issues, I don't think locking progression titles to just content progression alone is viable moving forward.