well dont make me laugh my ass off, firstly OT vader alone could beat ROTS presuit vader, why? because presuit vader goes apeshit, he doesnt think and he brutally beats his opponents, he hardly uses force attacks while OT vader on the other hand is far more experienced with the dark side and has a much wider range of force powers, OT vaders telekenesis alone could rip a huge tree which is not damaged in any way and throws it at roan shryne, Vader even used a waterfall to his advantage to distract the dark woman and yet he could destroy tanks on the battlefield as EAW proved, his force push is far more incredible than his predecessor pushing tark against gravity and smashs him on the ceiling while being able to push a thug in empire vol1 back many many yards, His lightsaber skills alone have improved and yet he can fence off 4 jedi at once while choking another
prehaps you should look at this quote
But even still, Vader wielded tremendous power and skill.
Heres one more
To counter fast-moving opponents, he would use the Force to pull out anything from his surroundings and fling the improvised missiles at his opponent. Without moving a muscle, anything from the venue of the battle could be used as a weapon to crash against Vader's opponents from all directions in a neverending barrage.
And another good one
Taking the proper lessons from his loss to Kenobi, he apparently learned how to control his emotions when in combat, finding a way to call upon calculated bursts of the dark side while not being blinded by emotions running amok.
heres the last Around 3.5 ABY, Vader had ordered ASP-19 droids, lightsaber combat droids based off the ASP-series droid, produced to fight him in sparring matches. They were faster and stronger than an ordinary man, and programmed with the knowledge of a hundred sword masters and a dozen fighting styles. Vader defeated them time and again, and ordered a new, improved batch of them. As his finesse improved they became too easy to defeat, even in a two-on-one match.
This is intresting
The Emperor, having gone out of his way to keep Vader alive, took an alternative viewpoint. Though it was true to say that he had not bargained for an apprentice "more machine now than man", Palpatine was of the opinion that most of the limitations on Vader's potential power were not physical but psychological. He believed that were Vader to fully confront his choices and disappointments, to completely shake himself out of his despair, that he would have been able to "reawaken the incredible power within him"