The only thing is, though, with the whole “he was training on Dagobah the whole time” idea, it doesn’t make any sense for Luke to wait a year to get clarification from Yoda and Obi-Wan about Vader being his father, or for them to wait that long to tell him. You could technically cut those parts, but that’d only work for a chronological saga edit (which is my preferred way of viewing the saga, but that isn’t universal) and you’d lose crucial character moments. I’d hate to lose, “There is still good in him” and “He’s more machine now then man, twisted and evil.” I at one point considered having a timeskip in which there would be an opening that took place right after ESB, Luke lands on Dagobah and confronts Yoda and Obi-Wan about the truth. Then it timeskips to a year later with the Vader death star arrival. But I realized timeskips don’t work for the style of Star Wars, as talked about in this video (https://www.youtube.com/watch?v=rD2G0D-nyLA) and would make it not feel like a Star Wars movie anymore. So really, to me, the only way it makes sense is to just keep it the way it is (except for rearranging the Tatooine scenes so Leia’s plan is first, then Luke’s, which clears up basically all the odd decision making) and have it so Luke is a more self-taught Jedi, lose Yoda confirming Vader is Luke’s father and the Obi-Wan conversation (unfortunate but doable) or just accept the idea that the Jedi masters refused to tell Luke more about his past and his family for a year (which just doesn’t feel right).
I already said this, but I think if the Jabba the Hutt sequence and the Dagobah sequence were switched around, it would improve the film structurally. For me, the Dagobah sequence sets the plot in motion and takes the film into Act II. I personally don’t think cutting Dagobah out would do any good for ROTJ. More likely, it would make it worse.