To use the example of Go, if you make the board bigger, you will have more options for making your move, and the game becomes strategically deeper.
This example has one critical problem, in that by expanding the board you do not create new types of moves a player can make, but rather the directions existing moves can be made in.
Which is exactly what I advocate: even if there is only one spell, there can be plenty of variety from how it is used.
Which only proves that despite what you opened with, my position is in fact, a fact.
Criticising my example doesn't prove your point. I really don't think you understand what facts are.
You've moved the goalposts. What do you define as a "new type of move"?
If you have the choice between a fire spell and a water spell, that gives you two choices. It you're given a third option (eg an air spell), then that adds complexity. Instead of having 50% chance of making the best move by accident, it's now 33%. You either have more choice and more complexity, or you have less. That's just maths.
The issue is balance. Was this particular enemy already vulnerable to air? The problem in this example is that in this case, having more options also means having increased utility, and that changes the balance of the game. That means rebalancing.
