I <3 all trek (well, cept Enterprise)... but the political moves thing very much did not start with Ds9 and VG. Having a racially diverse crew was a huge goal and point of emphasis of TOS... For example, television's first interracial kiss, one of the earlier sci-fi works that presented earth as being other than strictly white. It's kinda hard to see now, because at the end of the day a lot of the minority characters did end up as "tokens" (it kinda drives me crazy seeing Scotty's character get bigger as Sulu and Uhura's get smaller by the season) but TOS was perhaps the MOST political of all Treks given the times, and TNG is actually kind of the exception in that it didn't really push any boundaries in terms of non-stereotypical characters in terms of race/sex/etc.