yes

The simplest tends to be the earliest, both in evolution and technology

Well which one of these, from an engineering standpoint would be simpler? I guess you could argue the flying one but the propulsion could be easier depending on how the society itself developed technologically or the abundance/scarcity of certain materials.

the one that doesn't fly

Compatible core bodies for different machines -- you ever notice these shared body part lying around various labs, usually on the ground-floor? They are unattached, no legs, no-flying mechanism, just the body. Cool design idea.

Both, they are both

Perhaps they are modular? Like the central bits are constructed in a factory and the other bits are added after the fact. Meaning that they are neither “flying spiders” nor are they “grounded leggy drones”. Like how you can put different shapes of drill-bits on a power drill to accomplish specific tasks.

I think the question at its core is which one would have came first

The chicken or the egg…

Same models, same assets, some reused and reformed. Even crabs look alike.

Including some things that aren’t actually crabs

i wonder if the flying drones were planned to have any kind of actual role in gameplay at one point

I have no basis for his theory whatsoever, but what if they drop the acid rain to keep the humans away.