I don't believe that Vader's injuries weakened his force abilities
I keep hearing it everywhere about how Vader is a broken shell of his former self due to his cybernetics. If that's true then Starkiller (darkside ending) should be reduced to an apprentice level. He's more machine now than Vader ever was.
I don't buy it though. I believe that the connection to the force lies in the spirit and not the body. As long as some of the body remains (nervous system,brain) that will still allow that person to be who they are, their spirit will remain with their vessel and their ability to use the force remains the same.
I believe that Vader was always at the cross roads of dark side and light side and never came into his full dark side potential. Palpatine sensed this and declared him a broken shell. Darth Maul is an example of a Sith who fully embraced the dark side as did Sidious of course. If anything the armor and cybernetics should have made him stronger by giving him more hatred and pain that would have fueled his dark side powers. Palpatine should have eliminated all of Anakin's ties to his former life, strip everything away from him so he has nothing left but the dark side. Darth Plagueis did this with Palpatine. Palpatine should have remembered his master's lessons.