Roby, up-smash out of shield is simple (except with yoshi lolol). What I do is I press up on the joystick, then up on the c-stick. The reason it's harder for me to do it without c-stick is because to do it with A, you have to release the shield button before you press it (otherwise you'll do a grab every time). With c-stick, you don't even need to release the shield button, it will do an up-smash regardless.
shield --> joystick up --> c-stick up
shield --> joystick up --> c-stick up
