Common Lisp doesn't use (expensive) CLOS dispatch in the core language, e.g. to add two numbers or find the right equality operator. That's one known pain point due to CLOS having been "bolted-on" rather than part of the language which makes the divide between internal (using typecase and similar) and external (generic functions) dispatch pretty ugly; and gave use the eql/equal/equalp/etc... hell.
Thing is that you need a complex JIT like Julia's or stuff like https://github.com/marcoheisig/fast-generic-functions to offset the cost of constant dynamic dispatch.
I actually had such a conversation on that comparison earlier this year: https://lwn.net/Articles/1032617/