John Williams was pretty much washed up after Raider of the Lost Ark.
I strongly disagree about Williams, here. His work on the first three "Harry Potter" films stood out form his previous work I think. I thoroughly enjoyed the themes for Fawkes in "Chamber of Secrets" and some of the sweeping themes in "Prisoner of Azkaban" give me chills yet today.
Just to underline this: This really is just my perception of it. I wished I enjoyed the "The Lord of the Rings" soundtracks more than I do. And I appreciate that many people really love them.
It really can be difficult to describe how & why music affects us or the impressions it leaves on us. Music gets into a person in different ways from what we see. Since we're more used to describing what we SEE, it's easier to convey our impressions there.
It's funny, but I tend to think the same as you but opposite when it comes to Star Wars and LOTR. In Star Wars I tend to hear repetitions that I don't perceive as being intentional. Then again, Star Wars has two particular themes that are iconic in today's pop culture: the original opening fanfare, and the Imperial March. LOTR has nothing like that and very few other films have anything that significant if at all.
What I find in LOTR is a great variation that shows differences in cultures, in more ways than just notes. The instrumentation and choral works for Lothlorien have a distinctly Eastern influence, where as Rivendell is a different type even though both are Elvish communities. When a theme is repeated - such as the fellowship theme for example - it's done with variances in instruments and sometimes tempo, but it's done with a deliberate intent because the characters and story have changed.
Regardless, John Williams probably has a position that no other modern day composer will ever have in American culture at least. Much of that is due to Star Wars. James Horner has composed several of my favorite scores, such as "Titanic" and "Braveheart" and "Apollo 13". On that criterion he might be my favorite. Heck I even answered that on a Facebook quiz. I guess my answer of Howard Shore hear is a bit off the mark, in that it's Shore's work on LOTR that is my all time favorite.... but I don't count any of his other scores among my favorites