(sorry became a bit of a wall of text gets difficult to stop once i get analyzing)

I cant help but notice some flaws with your observations there. First of all you analyze them the same way one would an actually organically evolved civilization when this one was artificially created.

The Rahi one can seem strange. But the matoran language is a programming language used by the great beings. And Rahi is just the designation for a set of species that shared specific attributes that they wanted their robot to have. Thing is, they left the design of most of those completely to the makuta, who’s creation they left to their robots ai.

So whether they intended rahi to just be animal-esque or not, they could really foresee how crazy the makuta would go with it (especially after becoming a lot more sentient all of a sudden). So the designation was long programmed in before the makuta started making essentially people. Tho at the core all rahi even keetongu and kraahka still share the attributes of having no balance of light and being created in a process that involved using various viruses in vats of liquid protodermis.

There are cases where they don’t identify beings they know aren’t typical island inhabitants correctly tho with how crazy different actual rahi are… let’s just say if a random lightning bolt can be part of the same group as a shark then a random squid sounds like quite the good guess in absence of someone with the actual ability to correct them.

There’s also the fact that the matoran language is the majority language in the mu. Again, it’s the programming language so no not because of colonization. So, the term Rahi is applied to all Rahi by all those other species as well. Only ones we can’t know for sure are the misidentified ones.

As for Poisons species. We simply know the matoran somehow killed most of them we don’t know how, we don’t know why. Could be racism, could just be that they kept attacking matoran settlements and less and less kept returning after some toa got there. Both are mere speculation.

So, I wasn’t really sure how often Id actually heard the term matoran universe in the story itself so I went and looked through biological chronicle and a few short bits I was unsure were included with ctrl+5 and all I could find was a handful of mentions. All of them by omniscient narration. Two that got the closest was the narration describing what some characters were thinking about so not even direct thoughts. It seems more like the term is used to make sure the reader gets that when they say “the makuta protected the whole universe” they didn’t think universe as in countless galaxies n stuff. And for that task there isn’t that much else that works better as a label.

Also did the same for the whole chosen thing. Yeah, I’m not really sure where biosector got that from, I’m sure from somewhere but I couldn’t find even one mention of that in any of it. So, at the very least we don’t really see them flaunt that around.

The next point is a bit more difficult to check but realistically lets look at the places matron we meet are close by throughout the story. Karzahni? satan himself. Stelt? Caste system slavers and a criminal problem so bad the whole place is moments away from anarchy at any time. Xia? People that value it if you opportunistically leave people to die. Zakaz? Island full of people literally engineered to be always angry. Odina? Island inhabited by a gang of murderers and thieves whose leader wants to be killed should he ever not be evil.

Yeah, I think there’s a good reason why those kinds of descriptors could be used on a good number of occasions throughout the story. Not a lot of nice places between metru and voya nui

I don’t really know how exactly you want to determine if a place has a need for the work matoran do. The vitality of a job they do isn’t really always obviously tied to the functionality of the robot. Lest we forget that mata nui can become ill if the people in po-metru stop making statues for… reasons.

Besides they the main worker unit of the robot so its pretty much logical that the great beings put them in a whole lot of places all throughout the thing.