I can see that. Despite the slow pacing of the books, the last fight felt rushed. But more than that, it's possible such a metaphysical fight can never truly be expressed in words; we don't have the language for it. It will by necessity feel underwhelming, since the writing has to be done from a human perspective for us to understand and relate to it. As writers and readers we are imprisoned by our humanity and very limited perspective. This is why tackling such huge cosmic issues is difficult to do in a truly satisfying manner. Everything always sounds too human and not grand enough, because that is what we have to anchor it to. Like, say, I like reading sci-fi books about truly alien intelligences, but those are always creations of human minds, playing with human tropes. In the end, writing something outside human experience is impossible for us, lest what is written becomes entirely unintelligible.
I may be missing the mark here, but sometimes I have thoughts and they take flight. I just wanted to say that I can understand expecting more, even if I personally enjoyed the ending well enough.