I respectfully disagree with your assessment that the game currently is not this way. Most classes allow you to spam a few abilities and be somewhat effective, while properly knowing and executing rotations and expert use of abilities allows a player to separate themselves.You shouldn't have to watch videos or read verbose third party guides to learn how to play your class effectively. Maybe to "master" your class, but not to get up to a standard you'd call acceptable.
Diversity yes but not necessarily complexity, which is what I prefer.There are other ways to add diversity to classes than just lathering on more abilities that need to be countered by some other class's new abilities.
For me, I would prefer more niche use abilities. This is simply my preference of gameplay and completely subjective but I wanted to weigh in with a different perspective.