Well, I'm sure someone like Anchorhead would probably disagree and say that only the original Star Wars is the "main Star Wars material" and the sequels took liberties with the story that it shouldn't have. I'm not saying you're wrong, or that the prequels were right. I'm just saying that there are other viewpoints out there. Our generally collective viewpoint about the OT is just a viewpoint, and there's nothing really that makes our point of view more valid than anyone else's. I believe that our viewpoint is better than the viewpoint of the PT gushers, but that doesn't make it so. And I love the OT, but I can see the flaws it has, particularly the ones created through the revisionism that the sequels laid into it. Do I accept them and like them? Yes. And to a much lesser extent I enjoy the prequels, but I acknowledge the flaws and continuity holes in all of them. I can't give the OT a pass just because I prefer it and because its revisionism (mainly) got through much more successfully.
I think you can. The OT's later revisionism came as part of the same extended period of creative activity that started with the making of the first film. As long as that period continued, fucking around with the story was more justifiable than it was after Lucas had left the stuff for a long while and then returned with a different attitude. In effect, it was all a work in progress as long as it wasn't allowed to sit for long without being worked on. Whereas it was not so much a work in progress after it had been dropped for a while. I'm sure Lucas considered it a work in progress later on, but the intervening years gave it a status as a finished work of sorts, despite the potential for more films. And in the intervening years Lucas clearly broke with the Star Wars mentality he'd been in during the OT creative years, because when he returned he created work of a totally different mentality. This break in mentality, contrasting with the way the old films had much in common in mentality, underlines the validity of the idea of the idea of one creative period with one ongoing work, with revision justifiable within that period but not justifiable in a separate later creative period.
Furthermore, the very fact that the OT's revisionism resulted in a trilogy that works well is a point in favor of its revisionism, unlike the PT and SE's revisionism, which was destructive.
The later two OT films are far less easily divided off from the first film than the PT is from the OT. There was this long gap in time between the OT and the PT and when Lucas returned and made the OT he made films with a drastically different mentality from the OT. There are mentality differences between the OT films but not huge ones. Nor were there any many-year breaks between the making of the OT films. The PT and the SE were made after a long break and in a drastically different mentality. As such, they can be divided off from the OT to a degree far more than any OT film can be separated from the others.
Also, ROTJ far more completes the story than the first film. And while there were supposed to be other trilogies of films, the OT clearly establishes itself as one complete story within itself, despite its links to other potential trilogies. The OT does not NEED a PT to complete it. Sure, you're left curious about the backstory, but it's not necessary. But the first film very much leaves the story open and unfinished. Darth Vader not being killed off just shouts the need for a sequel. As does the unresolved romantic stuff and the beginnings of Luke's Jedi training. The unresolved rebel-imperial war could be left open at the end of a sort-of finished story, but the openness of it does further add to the picture of the first film being very much an unfinished story. But by the time of ROTJ's end we have a finished story. A sequel trilogy was never needed and the prequel trilogy, while always tempting, was never essential. The OT stands as one whole and stands well by itself.
So yes we can give the OT revisionism a pass while not giving a pass to the PT and SE revisionism.
But if somebody wants to take the first film by itself that's their prerogative. However, I think the OT-only approach is more valid. And both are more valid than any approach that acknowledges the PT or the SE.