How do you reconcile the version of Luke Skywalker we saw in the Mandalorian with the one we all know from the Original Trilogy?

I'm specifically referencing his lightsaber technique and combat skills in the Season 2 finale of The Mandalorian. The choreography was amazing, but it just didn't feel like the Luke that I grew up with. His speed and saber technique was so different here compared to the last time we saw him in Return of the Jedi that he almost seemed like a completely different character. Even after Yoda trained him, his swordsmanship was extremely poor during his final fight against Vader in ROTJ. He ended up just swinging his lightsaber around blindly like a baseball bat with absolutely no finesse whatsoever. Therefore it's hard for me to believe that his fighting style would change so much in just a few short years, especially since there were no Jedi left alive to teach him. Is there some in-universe explanation for how he became so good at lightsaber combat after the fall of the Empire, or do we just have to chalk this inconsistency up to the fact that the OT was filmed a long time ago and they didn't have the technology for proper lightsaber duels yet?