Lynch’s problem was runtime. It’s a mammoth novel; not in terms of page count - though it’s not slim by any means - but in it’s density. So much lore, character and story is crammed into it’s epic world building that it’s proven impossible to tell in a single sitting.
I’ve seen the long cut of Dune and tbh it doesn’t really fix this issue. Lynch would’ve felt these constraints from the outset and decisions made in scripting about what they could sacrifice for time. All those extended and deleted scenes can’t make up for what they couldn’t shoot at all.
Apparently a whole ton of scenes were dropped thanks to Lynch picking up an abridgement scene - the montage of Paul taking the spice, including the worms surrounding him in honour. Proves that necessity is the mother of invention, because it’s a great, pivotal moment only thought of afterwards.
Btw, my source for this is a great Youtube channel that does 10 minute reviews it calls ‘Renegade Cut’! E.g. 'Dune: Renegade Cut’. This was were i garnered that last nugget. Lots of Carpenter reviews too - the They Live one is pretty good.
Villeneuve’s choice to do it in 2 movies is the only realistic one and shows (if any proof were needed) that he intends to follow Herbert’s writing closely imo.
Though apparently Lynch had intended to follow Dune with a sequel, which explains the rather abrupt ending, which feels like a tease to more story. Obviously that never happened, which is why i hope Villeneuve is indeed doing it back to back.
Edit: Here ya go!