Yeah, even if he did lose some of his luster [which I'm not buying without canon sources] I doubt it would be to any sort of significantly degree. Vader still fought a number of times during that 2-3 year time span, including wrecking an entire Rebels base solo, while: casually tossing around ships, easily blasting through walls meant to tank shots from heavy artillery weapons, and taking apart a droid that utterly dwarfed him in size.
This was done literally months before ANH, IIRC.