All factions, the Ascendancy, Rayya’s Children and the Northern Alliance, descend from one common ancestor faction. The specialisation, so to say, happened some time ago (I would expect it to be in the hundreds of years, maybe a few thousands). So of course they’re not that different from each other; they have a common origin. We’re not talking about an Alien Nations scenario here, where you have Pimmons (frog people), Amazons and Sajikis (bugs) living on one planet somewhat peacefully due to an stork DUI accident.
So to expect any sort of major distinction within that small timespan is somewhat misled. I also don’t see any “political correctness” in this issue, but rather a diversification to freshen up the game. It’s visually more appealing to have individual hearthlings - skin color and gender are two relatively cheap to implement, but very effective ways of making units visually different.
It’s also no secret that SH uses a lot of RNG decisions. This starts with the gender of hearthlings, over their name, to what they look like (which includes body, hair, hair extensions, …), goes over the whole world and then every single encounter or animation that plays. They’re all separate, independent events that are not connected to each other. Only at the embarking, the stats can be somewhat dependent on each other to create a balanced town and avoid having a party full of “weak” or “strong” units.
There’s no ancestry or history like you would expect in Dwarf Fortress. The world you play in doesn’t have a history that you can uncover, neither do the units you start with. They’re all blank slates and it’s up to you what you do about it. For all that it matters, the game concerns them all as individuals without any connection to each other - at least, currently.
It’s powered by randomness in its vanilla state. If you are unhappy with that, you will have to find a mod that is removing some of that randomness with a more sophisticated, or even fixed/user customisable system. But that’s a can of worms because there are so many things that depend on randomness. If you start a new world, save it, and then play that save twice, chances are that it would differ the longer you play (although, I assume that if you played it exactly the same, then the game would be the same - as the PRNG returns the same numbers).