[SmG Battlefire]

Bear in mind that Harry is the last person to use the 3 Unforgivable curses unless he really hates the person. Even if he did, pretty sure Avada Kedavra is something he would never use. The Imperius is easily shrugged by Luke's force powers and the same can be said for Crucio since Jedi should be able to counter them (not completely sure on that).

Luke's knowledge in the force is still poor. Heck he didn't have real Force training. Yoda only tought the very basic of balancing the Force. Other than that his Force is weak. Now if you had Obi Wan that would be different.

Again Luke is a weak Jedi. He didn't defeat anyone powerful. He only beated Vader because Vader was old and weak. Vader even stated in the archives that he is was weak and any Jedi with minimum skills in the Arts of the Light Saber can defeat him.

Compare Luke to someone like Revan. He is nothing.