Although I haven't read much pre-Tolkienian fantasy, I did find this article about British uses of Norse myth before JRRT [EDIT: this used to link to Andrew Wawn's lecture
Philology and Fantasy Before Tolkien at the Sigurður Nordal Institute, which is no longer online]. I think that what this points out very clearly is that the re-use of Germanic mythology, often combined with a rejection of modern idiom, was already well established and popular long before Tolkien began to write. In terms of language, what Tolkien seems to have done is to adopt a far more readable form of 'watered' archaism than some of his predecessors. William Morris in particular sometimes allows his own learning to get the better of him, and on those occasions his prose becomes either completely unreadable without a Middle English or Old Norse dictionary, or so cumbersome that it loses all beauty. His style may have been what Tolkien had in mind when discussing
correct word usage in Beowulf translation, although Tolkien did have good reasons to think well of Morris in general.
Of course, William Morris' generation was caught up in the flush of newly discovered territories of myth, legend and history that were being opened up by the emerging science of comparative philology. The excitement of people brought up on Classical myths on finding another legendary world far closer to home can only be imagined these days, but the reactions of contemporary authors survive in often surprising works of fiction and historical romance. What has changed since Tolkien is that reactions to this material have tended to follow him, in that many authors began to write in that style who knew nothing of Ing or Finn, the Wulfings or the Nibelungs. Their reactions were to the same material, but as seen through Tolkien's vision, so that Tolkien replaces his beloved northern myths as the emulated source. Alongside this motive is the legacy of his popularity, which makes him difficult to ignore, and which presents the eternal temptation to react to his work.
Since this is really not my area, I'll leave others to continue the argument. To my mind, Tolkien fits into a long tradition of English writing that stretches back into the Anglo-Saxon period, and which revolves around imaginary landscapes and strange adventures among supernatural beings. That many people respond so his work so strongly suggests that there is as much a taste for such writing in the modern world as there was in the Middle Ages, and fully justifies the earlier work of the storytelling philologists and the dream-weavers of the fantastic who were Tolkien's predecessors.