When you are doing client site where slider has a fixed place, then yeah, doing it via CPT may not make sense in such case. But client theme and mass distributed theme are two different animals with different needs.
Anyway, you obviously know your WP, so let’s agree that both approaches make sense:) My main point of the thread was do not use Theme Options, use WP Customizer. How you approach the slider is not that important, just make it simple for end user.