I think that well defined rules for combat roles are great. You are a controller that dazes. You are a defender that attacks multiple foes. There can be a little bleed over, but the controller really cannot defend too well.
I think that well defined rules for non-combat roles are extremely questionable. You are an sophisticated infiltrator that only does this via guile. Because of your role, you don't infiltrate via stealth. That's a different role.
In this example, a guile-infiltrator and a stealth-infiltrator are two different examples of the same role, in the same way that a paladin and a fighter are two different examples of the defender role. The whole point is that, a GM can look at a party and be assured that, if there is an infiltrator, that character will be well equipped to handle infiltration challenges.
You just named 7 non-combat roles off the top of your head. There are 4 combat roles in the current game. I bet you can come up with 30 or more non-combat roles.
That's not quite true. I bet I could name over 30 non-combat "classes". Once I did that, I would try to group those classes into roles, the idea being that two different "classes" in the same role should be potential substitutes, in that they could both perform the same types of challenges, but also complementary, in the sense that they approach the same types of challenges in different ways. I'm not sure how many groups of abilities (i.e. "roles") you come up with, but it's much smaller than the number of concepts.
Non-combat roles are different from combat roles in that the balance is much more game dependent. In each case, the objective of giving characters roles is to make sure that the "spotlight" is fairly divided among the PCs. With non-combat roles, the usefulness of the role (and how much "spotlight" in brings) is going to be heavily dependent on the type of game that is being played. For example, an "explorer" role might be unusually useful in a Kingmaker game due to the high amount of wilderness exploration, whereas a "face" role might dominate in a more social game.
That said, non-combat roles are a little more self-balancing so long as the players have a good understanding of the campaign. Sure, a "face" role might be super-useful in a court intrigue game, but multiple PCs are likely to take a "face" role in such a game. Those PCs will end up dividing the "face" spotlight, which mitigates the balance problem.
In a split of combat and non-combat feats and potentially roles, PCs are somewhat forced to be semi-decent at both. They cannot lean in one direction or the other too much. That takes away from the game instead of adding to it.
That runs counter to my experience. The games I've played have been stronger by forcing the PCs to be semi-decent at both combat and non-combat. Both combat encounters and non-combat encounters can be quite long (in real time) and they tend to "chunk", in the sense that you can have many hours of playtime without significant combat but that, once combat begins, you can be fighting things for many hours as well. I think the game is stronger for making sure that each character is equipped to participate in both aspects of the game.
Yeah, you can create a dumb barbarian that just drinks and fights, but someone playing that character is going to be seriously bored between fights. Far better to play an dumb barbarian with a canny eye for danger and expertise in navigation and survival.
-KS