Yes, I made a forum account just to respond to this.
The first topic I'd like to address is "prolific(ity, ness?)." I'm wondering if I missed out on some of Lewis's work--given, I am American, and British literature is not as easy to come by as copies of Hemingway and Faulkner, or even Fitzgerald--that being said, I think there's a slight discrepancy between "work published" and "works composed". Tolkien's son later dropped all of Tolkien's written backstory, giving us books like the (pardon my spelling, I'm too lazy to look it up at the moment) Silmarillion and innumberable "Untold Tales" volumes. In addition to these were various Old English stories translated and published (seen in America only under academic light, otherwise not readily available) by Tolkien, including Sir Gawain and the Green Knight, the Pearl, etc.
The second is "credibility". While Lewis did write various essays themed outside of fiction, and worked allegory into the Chronicles, I do not feel he was as devoted to storytelling as Tolkien was. All of Tolkien's books come in the style of a well-versed oral tradition; he was, and intended to write as, a storyteller only. Lewis, like has been noted, was whimsical in his pursuit of a coherent/cohesive storyline, but expressed himself magnificently in his essays/letters. I think that to compare them in each field in a "who's better" manner is silly. It's like comparing Bradbury and Vonnegut--both are going for two very different goals, even though they use the same genre and similar style.
The third and final issue I would like to speak on is "friendship". They were bros. Sure, bros grow apart, but all bros do.
And we, as educated and thoughtful individuals, can remember them as bros, even if we know that like all other bros, they fell apart towards the end.