You neglect, of course, that David Lynch, himself, sought to distance himself from the movie, considering it something of an embarassment, and requesting an Alan Smithee [1] credit for at least one version of its release.

In some ways, we can look back on it with a sort of "so-bad-it's-good" a e s t h e t i c in mind, and when understanding David Lynch's sensibilities, you can still catch a glimpse of his creative influence shining through. But really, David Lynch is ultimately correct in his self-effacing critique. It's kitschy and campy in a lot of ways. Just watch the closing credits in isolation, if you don't agree, and try and challenge that opinion again.

To understand what I'm talking about, watch Dune, then watch Eraserhead, and then watch Dune again. Eraserhead informs us of David Lynch's purest intent realized as a feature presentation.

You can see some of Eraserhead in Kenneth McMillan's portrayal of Vladimir Harkonnen (and indeed, it's the scene that Jack Nance [3] appears in), but that's really about it. That Dune doesn't live up to the visualizations of Moebius' imaginary realms [4], and that much of the budgeting, politics and film making technology of the day stood in the way of the final theatrical release is probably what bummed David Lynch out about it.

[1] https://en.wikipedia.org/wiki/Alan_Smithee

[2] https://www.youtube.com/watch?v=YRzVFlZxBv4

[3] https://en.wikipedia.org/wiki/Jack_Nance

[4] https://en.wikipedia.org/wiki/Jean_Giraud