He grabs onto the railing to prevent himself from falling. What more do you need explained?

He is noticeably weak here and holding off Luke with his other hand with the saber in it. He looks like he is trying to rise to his feet but is too weak to do so under the fury of lukes angry attack.

Any way Luke is using the darkside here to over power vader.

If it was luke versus Anakin in Episode III luke would still win. I have no idea how vader won in empire strikes back if you think the anakin of the prequels is in the suit.

I mean starting with Jedi Vader became a pussy. He also gets owned by Dooku in Episode II when he was anakin and when he is vader in episode III by kenobi. He cuts obi wan down in episode IV only because ben lets him to create a distraction so our heroes can escape. He even gets owned in the force unleashed by Starkiller.

Nice pink bubblegum screen caps there by the way,lol. His saber is red in the gout. The 2004 deserves to be thrown in the trash bin. Pink Lightsaber. Hayden in the ghost scene. Jar Jar, and Jedi Rocks.