I'd counter that there is one over-riding focus of the game:
Playing the role of a particular individual.
As I said, the base elements of race, class, themes, backgrounds would provide you with the ability to participate in all aspects of the game
to some degree. However, beyond that point or if you went really in-depth in your character creation, you could focus yourself on one aspect.
A
realistic humanoid character is going to have more skills than simply "swinging a sword" and even that ability will translate into some other skills that are useful outside of combat. Playing a guy who can only swing a sword, which obviously should be an
option, does not really do well for generating a believable character.
The three segments you offer are quite real and all fit within that focus. But if a fixation on balancing those three segments overrides the original purpose then you start getting into the territory where people are unsatisfied because the experience becomes to close to be a board game with carefully balanced functional tokens. You can still talk in funny voices as you move the tokens around, but if the tokens put functional balance over being the person it doesn't really matter.
I'm not interested in balance in these areas. I'm fine with X class having more combat ability and Y class having more social ability. Of course NO class should have 100% in all three areas, but at the end of the day if the group builds a diverse party, they should roughly be able to cover all the bases. That
could come in the form of a party that is 100/0/0, 0/100/0, 0/0/100, or it could come in a form of 50/20/30, 20/35/45, 10/10/80.
IMO, as a default, no class should be 100/0/0 or 0/100/0 or 0/0/100. There should be some base spread to give players some ability to partake of all parts of the game, and allow levels of customization to adjust those numbers.
In the end, both in fiction and in the real world, not every character is going to contribute equally in every scenario. If you want everyone to always contribute then you are proactively undermining the effort to create a great experience of feeling like you are inside the scenario. It is perfectly understandable how equity of contribution (no call for perfect equity, I understand) would be appealing in its own right. But don't tell us we should give up something much more important just to gain that and we should call it a good thing.
To much equity is expressly wrong for role playing as I see it.
You are welcome to completely reject my goals. And for all I know you are having 100 times the fun I am. But don't tell me you are doing the same thing as me and at the same time advocate undermining the core principles of what I'm doing.
As I said, I'm NOT suggesting every character gets to participate equally in all aspects, that's unrealistic. I'm just saying that every character should have some default ability to participate. No class should say to players "If you play this class, you can't play 1/3rd of the game." In a typical dungeon for example, the mage is the go-to guy for dealing with magical impediments(knowledge: arcana/use magic device), the fighter is the guy who'll keep you from getting lost or tell you what stone to hit to bring the place down(dungeoneering), the rogue will help you avoid dying to hidden stuff(find/disable traps) and the cleric will help you know if the glowing gem you just found is actually a portal to hell or just a glowing rock(knowledge: religion). Each character is skilled in a different area, but over the course of the dungeon, all of them were able to bring something useful to the table
besides combat ability.