Every class is useable for casuals though. You can clear every single casual content without ever thinking about your rotation. I have done expert roulette with smn without phoenix-bahamuth (not proud of this hah) and no one ever batted an eye.
And just because you play the game casually doesn't really mean that something having a bit more of room for optimization and actually make your brain think is bad. Personally, I hardly do savage/extreme and I despise this type of narrative.