An interesting idea, but I genuinely don't see how that's supported by the movies? Ignore this if you were just joking!
Hmm, it could be possible. What if the tree network is the true home of a Navi's mind? Wirelessly controlling a Navi body is possible, since that's what the main character does. After body death, the mind doesn't move to the tree network, it just stays there. Perhaps it wasn't so hard for humans to invent the avatars, since it's close to the natural function of the species. Perhaps the Navi have very small brains, which added to human biologists' disdain & racism, not realizing that most of their neurology is hosted remotely.
Huh. Good theory. I didn't consider that, nor have I heard anyone else mention the idea elsewhere.
I can't recall any evidence from the movie(s) that would disprove it. It could be a plausible plot twist later. We don't see humans pilot human bodies remotely, but then again, why would they bother? At least I recall that the soldiers revived from backup, like Quaritch, were directly downloaded into avatar brains with no remote control. From a hard scifi perspective, human remote sleeves would be handy to have. Maybe the tech was invented late, maybe it's too expensive, or is comparable in cost to growing Avatars. Sully couldn't afford treatment for his spinal injury, it was offered as a reward by Quaritch, so regenerative medicine might be very expensive.
What if Avatar isn't actually about environmentalism vs. technology, but about recognizing superintelligent infrastructure when you see it? A deep dive into why Pandora's "natural" ecosystem looks suspiciously like a planetary-scale AI preserve, complete with biological USB-C ports, room-temperature superconductors growing wild, and a species of "noble savages" who are actually post-singularity retirees cosplaying as hunter-gatherers.