This allows you to shrink the language syntactically, but not semantically. For instance, you can make it so setf isn't visible from your own package, but you can still call out to functions in other packages that will modify lists, so it's not suitable as a way to reduce the conceptual overhead "things you have to worry about when using lists".

If you really want to go hard-core you can unintern all the symbols in the common-lisp package.