This seems like a consequence of the language never getting another standard. If it did, and given the way Common Lisp systems work, I think there could've been something like cl2 and cl2-user packages which could've pushed more towards that generic style that CLOS promotes, and maybe eliminated some of the elements that were redundant or didn't quite fit with everything else (is it `(function sequence index)` or `(function index sequence)`?). Those conflicts make sense given the history of the language (it was created to help connect several branches of the lisp family). And the older standard would've been easily preserved in the cl and cl-user packages.

But the language is essentially frozen in the existing standard, and can only be extended by community consensus right now.