One of the things I like about a lot of the older pre-2000s western fantasy is it feels really refreshing after reading fantasy web novels and light novels since a lot of the tropes you see in Japanese fantasy light novels are nonexistent or in fact the opposite.
Interesting opinion. What kind of tropes have you seen in fantasy novels? Do you mean just eastern novels and such? I'm not so sure that Western novels have them.
Nah, I don't think Dune or LotR or any other similar series would make good manga. No one would like literally hundreds of pages with zero action and just "blah-blah-blah". Well, you can of course drop out all that "blah-blah-blah" but then it wouldn't be Dune/LotR/whatever.
That's true, but I feel that a skilled adaptation would adapt the long-winded moments into something more suitable for the medium. In Dune, I feel the scene that most often gets this treatment is the dinner scene. It serves to show the relationships between power-brokers in Arrakis, and also to show off the way that the Atreides strategize in such social gatherings. I feel the 2021 movie adequately shows off how the clan works as an organization by having them frequently communicate with handsigns and such. The local politics not adapted and I feel this is a better choice since it didn't matter in the long run.
For LOTR, I imagine you're referring to the long winded travel segments. Could just be adapted into two-page spreads showing off the landscape and the enormity of the world in comparison to the small party.
Responding to the thread's question, when I was in school I read a book. It was called "Durante la Reconquista" by Alberto Blest. In English it's "During the Reconquest", which refers to the moment after Spain had gotten rid of Napoleon's brother on the throne and turned to taking their colonies back. The book takes place during this historical period in Chile and is about a rich family's struggles during, since they were not royalists. Protagonists has his edgy backstory ("they killed my family!"), a love triangle with a hot MILF and his childhood friend (who might or not be his cousin, now that I remember), a merry band of revolutionaries powered by friendship, bishounen antagonists, etc. Anime-related tropes abound. When I was reading I couldn't help but to think it would be a fine manga, or anime. Could even it give it the Monte Cristo treatment and make it into a sci-fi manga. Optimally, an adaptation should have that LOGH styling with a bit of a romantic bend to it.
Still, it is far-fetched to expect a japanese mangaka to know of a relatively obscure book even in it's country of origin. My countrymen would mostly regard it with an eyeroll, since most were forced to read another book by the same author with all the emnity that creates.