Again I don't see how it is definitely the case that vader's saber fighting is weaker then Anakins. Yes he lost midi's, and yes he is in a suit, but as I said before, physical attributes have nothing to do with fighting. It's all in the force. Yoda can barely walk, but nobody can keep up to him in a saber fight aside from palps (who was strained to do so imo). And isn't it funny how the only guy that can keep up to him, is also a decrepid old man who probably couldn't do 1 pushup let alone flip around and jump like he does. When saber fighting, you let the force totally overtake you, and your physical limitations become irrelivent with enough training.
No, vader being in the suit has nothing to do with it I believe. In fact, as we have seen in star wars, technological limbs and suits, such as Anakins hand or grevious's suit, can actually work better then they did as biological.
So that only leaves the loss of midi's. And I personally believe that someone with 20,000 like Anakin who is massively inexperienced, would be defeated by someone with 15,000 who is wise and powerful in the force. Obvious example being Obi wan defeating Anakin. Obi wan has far less midi count, but he won, with experience, smarts, patience, and more force knowledge.
20 years of training in the force for mech vader would certainly make up for the loss of midi's. What good are midi's if you aren't trained properly anyway?
Mech vader would defeat Anakin in a duel IMO.
Mech vader (as we see in OT) adopts a technic much similar to samurai fencing. A kind slow but very effective. Luke fights like his father pre suit. I agree with the opinion that years of meditation and training, turned vader very powerful. It would do the same with him, even if he didn't went into the suit.