As a big fan of Jodorowsky (L'Incal is one my favourite graphic novels ever), I think we could also unequivocally say that whatever he had made would
not have been very faithful to the book. It's quite possible that Dune fans would have been even less happy with Jodorowsky's film than Lynch's.
We also have to remember that this was before Star Wars and Alien. Most scifi at the time was, with some honourable exceptions (2001: A Space Odyssey, Silent Running, The Andromeda Strain, Solaris), pretty silly, childish, often campy stuff: The Black Hole, Buck Rogers, Moonraker. Pulp origins aside, Star Wars introduces a level of violence, maturity and realism to the genre that stood out at the time, and closer to that of contemporary adult 1970s productions like Apocalypse Now, Easy Rider and so on.
For all the considerable talent involved in the Dune adaptation, it's quite possible — and this eases the pain over the loss of the project a bit — that it would have been closer in tone to something like Zardoz or Flash Gordon, i.e. a big, colourful, but ultimately also a bit silly extravaganza. Even O'Bannon's Alien script was also pretty pulpy and silly until Ridley Scott, David Giler and Walter Hill hammered it into shape.