Ok, first off a few things:
1) While ZOS call it sub-classing, it's really multi-classing - I shall be referring to it as multi-classing for this thread
2) DLC classes have distinct skill lines (Tank, Heal, DPS) but base classes do not - this makes the multi-classing system inherantly unbalanced
3) The current end-game meta is so much more powerful than the next best it destroys build diversity at end-game
4) Multi-classes are more powerful than Pure-Classes
The problem with balancing that is that to do so currently would require nerfing classes to make class combinations less powerful, but then the pure-class would also be less powerful and still not stack up against a multi-classes. So,
Q: How to balance an inherantly unbalanced system and restore build diversity at end game?
A: By introducing actual sub-classing - being further specialization into a desired role.
A role specialization system could be used to provide buffs to pure-classes bringing them into line with multi-classes, as well as giving the necessary power and tools to compete at end game without destroying class identity, and increasing build diversity at end game. Base classes could be given extra perks to offset the differences caused by not having seperate skill lines. Something similar to how the CP system operates with passive and active buffs that need slotting.
It would give the player more choice on how to build - between multi-classing or sub-classing - with either choice being competitive. The more you multi-class the less you can specialize.
It would be entirely up to the player on which route they take.
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