I want an official response.

[Amused]

Well, since you aren't required to buy them to play I'd say they are in fact optional. I think those who feel the absolute need to purchase things from the cash shop are in the very extreme minority and also maybe need to think about their habits and choices in real life.

You aren't "required' to buy anything, technically. Whether they are optional or not is entirely subjective and dependent upon the person and what aspects of the game they enjoy.

Minions are content?

Yes, they are. Everything that exists within the game is content.