I think it is. A lot of the 'stagnation' is due to the fact that the standard is a standard, so Lisp implementations aren't changing the definition of characters willy-nilly — and so code written twenty years ago is still correct and performant enough, so there's no need to update it.

I would love to see a slightly more modern CL, but it's good enough to get work done, and it's still light-years ahead of everything else.