Legion is the least casual friendly expansion since Vanilla. It has by far the highest ammount of grinding since Vanilla, it has by far the highest level of content since Vanilla and it's arguably in many respects the best expansion since Vanilla (though certainly not my favourite)... But is it casual friendly? Depends how you define casual, but the way you define casual in my eyes makes Legion pretty unfriendly to you.
If it's not clear, Legion is designed around grinding heavily in a way that no expansion has done before. Think Diablo 3 loot farming and Paragon levels dumped into WoW, that's Legion.