When we look at all the TES games, we could use all at once. Healing, destruction, mezzing, Combat in all forms. And not being restricted to two weapons.
You can tell me what you want but two weapon sets is no variety. I have created all combinations possible and the outcome is more or less the same that it's yet another illusion: Some builds work extremely good while the majority is total lackluster.
If you enjoy playing rather unviable specs, just for the sake of seeing yourself as a special snowflake - then go for it, bathe in yet another illusion ontop of it all. I want plain hard facts.
When you look at Foundry, speak to veterans, fact is that ca 20% of all possible combinations have real vallue to it, while the other can be replaced by said 20% in no time. Reducing the presented variety to a bare minimum, WHEN you look at effectivity. Bow-sorc, Sorc-healer, DK with a destro staff leading the pack of 'the' most effective specs.
Now lets contemplate about the possibility of adding the feature with lvl 50, to yet give the player more endgame options, to add another Class to his own arsenal. Getting all Templar Features as Nightblade, or for a Dragon Knight adding Sorcerer. This is real variety. That would create even more options and lets be honest the chances are huge that we get more builds that actually work as the current ones.
Forget class balance, even in this state how everything is now - there is no real need for class balance because all abilities across the board are somewhat balanced. There are some spikes but some spikes are okay for everyone.