Did we ever see a single Alien Admiral in TOS? Or any Alien Captains? Hell, aside from Spock I'm hard pressed to remember any Non-Human Starfleet Officers.
TAS had Arex and M'Ress, and ST:TMP had Ilia and a bunch of alien crewmembers in the background.
But it's true that the shows have done a poor job depicting diversity in Starfleet. The only alien admirals we've ever seen in canonical Trek are three or four Vulcans and one Bolian, all but one of whom appeared in DS9. And the one Vulcan admiral we saw in TNG (in "Conspiracy") was possessed by an alien bug thingie and died.
Except Hikaru isn't a "pan Asian" name, it's specifically Japanese. There are names that are pan Asian, Ming would be one example, it is found in many Asian counties, Hikaru isn't.Uhh, what? Japan is certainly part of Asia, so a Japanese given name and a Filipino-ish surname suggests a mixed Asian ancestry, exactly as intended.
You're taking "pan-Asian" too literally. It's not that every single thing about him had to be generically Asian, just that he came from a mixed background. Yes, Hikaru is a Japanese name, but Sulu very much isn't. The name as a whole is mixed, and that's the point.
The best reference source for what the creators intended is usually The Making of Star Trek, which was published during the show's run and was written by a journalist with extensive access to the production. It says of Sulu (on p. 247), "Although of mixed Oriental and Filipino background, Sulu's cultural heritage is mainly Japanese." Certainly we saw this in "Shore Leave," where he conjured up a samurai (and seemed oddly frightened by it). So it's not that there's anything wrong with including Japanese elements in his background, it's just that he wasn't meant to be purely Japanese, as is evident from his surname.
George Takei and Vonda McIntyre are not TPTB, it was Nicholas Meyer's decision that enter the name into official canon, and Meyer definitely is part of "TPTB."
I get sick of people using "TPTB" at all. It's an invocation of some faceless amalgamated "Them" on whom all complaints can be blamed. It's essentially a stereotype, substituting a generic faceless foe for individual human beings, and that makes it an intrinsic fallacy of thought. We should attribute decisions to specific individuals and understand their specific motives. Trying to avoid contemplating details and reduce everything to simplistic buzzwords is intellectually lazy and inimical to truth.
Anyway, "The Powers That Be" are supposed to be the entrenched authorities who run the whole show. Nicholas Meyer was a director on only two movies and a screenwriter on three, with no direct influence beyond that.
And there is no "entering into official canon." Canon is a term coined by fans and critics to describe the original work as distinct from tie-ins and fan fiction. There is no "office" that "enters" things into any kind of formal record -- there are just people making movies and TV shows. They never think of them as "canon," they just think of them as the current job they're doing. Takei suggested using the name as a nod to Vonda McIntyre (who I believe was with him on the set that day), Meyer shrugged and said "Why not," and that's all. It was an offhand improvisation. Calling that "entering into official canon" is needlessly pretentious.