Finn was pissed in the lightsaber duel as well so I don’t find it to be to unbelievable that he got a lucky hit in before Kylo demolished him.
Couldn’t Vader have just used his mastery of the force against Luke in Bespin… why bother dueling him with a lightsaber at all?
Good question. Darth Vader (even in the OT) is a Master of the Darkside and he could have easily choked Luke unconsciousness, threw him in the Carbonite Chamber and that should have been all she wrote. But the plot demanded that a duel take place so that Luke could be told who his father was. And I don’t see much wrong with that.