Aren't two things being confused here, anyway?
1 - Moorcock doesn't like Tolkien's way of writing and
2 - Moorcock doesn't like Tolkien's politics.
I have to say that many books I've disliked politically I also felt were badly written, but I'm sure that someone whose politics I don't agree with 100% - le Carre, say - could write very well. The problem comes, I think, when the need to make a political statement twists the truth so that the portrayal of whatever reality - even a fantasy one - isn't convincing. But I don't think Tolkien falls into this trap. I have problems with Tolkien, but most of them are about his writing and his interest (which is his right as the author) with things that I find dull, such as songs.
With all respect to Moorcock, Elric’s singing slaves just sounds kind of silly to me. It’s arch-villain stuff (Wuh-huh-huh!). I find Tolkien’s view – effectively, that all things are moving towards their end – far more unsettling because it’s not there to show how “dark” one character is – it’s basically true.