Then again, TOS blends right into TAS, which in turn gives the impression that nonhumans have long (since the beginning?) been standard aboard Starfleet ships. TMP then maintains the format of lots of latex aboard the Enterprise, setting the example for the remaining TOS movies.
It could be that Starfleet largely segregates its crews, for practical reasons, and that Kirk in TAS and TMP had his turn as the captain of the token "mixed" ship that the Fleet maintained for political reasons. Or it could instead be that Pike had run an exceptionally segregated ship (perhaps out of racist reasons), which Kirk inherited for his 5-year mission and only slowly transformed into something more like the Starfleet norm.
Timo Saloniemi