i read somewhere a while back that the consensus in literary circles is that tolkien was not a fiction writer (in so far one can reach a consensus on such a thing). the reasons they gave are pretty much what you say here. but his books became first a cult classic, and then...somehow...or the other...infiltrated mainstream consciousness.

he wrote during a time of great societal turmoil that marked the end of an age, and my personal theory is that the dense and turgid prose was actually exactly what people were looking for. the prose is exactly what a layman would imagine an ancient document about bygone worlds would read like, and if the world as u know it is collapsing around u, it can be very comforting to read something like that.