Slickness can signify in two ways, I guess.
People often complain about Blue Note post-Sidewinder having a formula. It's only half the story (sadly, no Grachan Moncur boogaloo grinders out there). But certainly, a lot of Blue Note records from that era are quite 'formulaic', and sometimes can feel like so much product.
On the other hand, the production choices are much more noticeable on CTI's records than Blue Note's or Prestige's or even Mr Taylor's productions at Verve. Much more noticeable and much more noticeably expensive.
On a record-by-record level, CTI is surely the "slicker" sounding product, even if Messrs Lion and Wolff, arguably, had their own slick approach to business.