I'm not terribly clear about what the assumption is, exactly, and I'm not sure everyone in the conversation has the same referent for it, so rather than say "yes" or "no" to an ill-defined question, let me articulate some related thoughts.
I like the idea of fanfiction where characters who in canon think and behave in muddleheaded ways and ignore what seem like fundamentally interesting aspects of their world instead think and behave clearly and attend to the interesting things.
If done well, rationalist fanfiction can be a great example of that, as rationality is a very useful tool for focusing one's attention on the things that matter. I like that sort of rationalist fanfiction quite a lot. (Which is not to say that I like anything that qualifies as rationalist fanfiction.)
MoR explores some marvelous ideas, it's clever, it has moments of genuine humor and genuine human feeling. The early chapters, in particular, really spoke to me; the later chapters less so. As fanfiction goes, it's probably in the top 10% of what I've read in my life, not that I'm a huge follower of the genre. But it has weaknesses that frequently bug me. As fiction goes, I would be fairly disappointed if I'd picked it up at a book store. I don't care too much about Americanisms vs. Britishisms, though.
I'm vaguely intrigued by the LOR variation -- it reminds me somewhat of the Sundering novels -- and might read it some day when I have more time to spare.
Dunno if any of that is relevant to your discussion. If not, feel free to ignore.
The other plus point for MoR is that J.K. Rowling is not that great at shaping sentences unsupervised. I only continued past HP book four so I could find out how it ended - books 5-7 serve mostly as cautionary examples as to why immunity to editors is not such a great idea in some cases. Possibly I am oversensitive to appalling sentence construction, but then again if I'm reading something it's my own responses I'm most interested in.
JRRT's sentence shaping is way better than JKR's and the English translation of this Russian fanfic is not too bad (allowing for grammatical hiccups) - different to JRRT, but not clearly better.
This may be old news to some people, especially the Russian speakers, but I didn't see an article about it here.
In 1999, Kirill Yeskov, a Russian paleontologist, wrote The Last Ringbearer, a 270-page take on Lord of the Rings from the point of view of a medic in Mordor's dying armies who is also a "skeptic and a rationalist." In fact, Mordor represents the forces of reason in this retelling of the story. As a Nazgúl (himself a former mathematician) explains, Mordor is "the little oasis of Reason in which your light-minded civilization had so comfortably nestled." Barad-dur is "that amazing city of alchemists and poets, mechanics and astronomers, philosophers and physicians, the heart of the only civilization in Middle-earth to bet on rational knowledge and bravely pitch its barely adolescent technology against ancient magic."
The story has been newly translated and is available in free PDF form -- in English and the original Russian. There's a recent review from Salon as well.