There's not a single class that is difficult to learn in that game. Seems you never played Kensei because their feint system is pretty simple. The thing that takes more time is knowing every class move and learn to counter them with your moves. Know what works and what does not. Then learning to deflect/parry/counter gb is something you gotta learn with every single class and what takes more time I think, but if you have good sense of timing and good reactivity you can get good pretty fast.