There is perhaps an argument to be made that, casting requirements and makeup concerns aside, there is no reason why the "races" of the humanoid aliens in the Trekverse should mirror those of humans (or even worse, whatever humans are easy to snag in SoCal or Toronto).
Not sure I understand what it is you're saying here. By use of the word, "mirroring", are you referring to "white" aliens played by white actors and "black" aliens played by other white actors?
ALL of the Aenar in Ent were played by white actors? Didn't know that. Of course, this was still Berman/Braga Trek.
From what I gather, the issue isn't about whether or not extra diversity is a good thing or not. No. It's that the PR for DSC likes to pretend that it has the "first racially and gender diverse cast" for Star Trek or "first time serialization is used".
I roll my eyes whenever clickbaity ""news"" articles would lead you to believe SMG is the first African-American actor to even be in Star Trek! That's not very fair at all.
I haven't read a single article, or heard a single interview by DSC cast, crew, or production staff, that states or implies that DSC is the first Trek show to display a racial or gender diverse cast. Nor have I read any articles that state this. Most reporters I'v read seem to be aware of the previous show's histories on diversity. If you really have, please provide a cite.
What may be confusing you is the fact that DSC
is the first Trek show to feature two openly gay human male characters as part of the regular crew/cast. Or perhaps, even though DSC is not the first Trek show to feature a woman of color, it is the first Trek show to present one as the main protagonist.
Overall, I'd say that makes DSC has taken diversity in Trek to a new level, and from what I'm reading lately, it seems that they are planning on leaning into it even harder in subsequent seasons.
As for serialization, again, what I'v read is DSC cast and crew mentioning that DSC isn't the only serialized Trek, but is the
most serialized. This is especially true if you compare first seasons of all the spins.
As I wrote earlier, Voy was serialized like the X-Files, overall arc (returning home), which they touched on periodically, with most other episodes being standalones. Ent's last two seasons were highly serialized. DS9 was similar to Voy with it's Emissary arc, but became serialized in the last couple of seasons.