Not sure I agree. As we see with Avatar, the technology was easily able to mine large swathes of the land and where it faced any real difficulties, bomb the heck out of it.
For Pandora, yes.
But Pandora's ecosystem wasn't that crazily deadly (didn't seem much worse than Ice Age Earth would have been, predator-wise) ... and it's nothing compared to Midworld. Pandora doesn't have any superdeadly immune-to-everything megapredators (that we saw), like the silverslith. (It's said that no one has ever seen one bleed; when one attacked a group of 30 men and 30 furcots only a few were able to escape alive (and totally unable to hurt it) [furcots are basically super-grizzly-bears with 6 legs and human level intelligence, but stronger; one knocks through 3 feet of superstrong concrete later in the book]; the instant-death nerve poison the people use is totally useless (supposedly because it lacks a nervous system, plus its skin is too tough to pierce anyway), it never sleeps, etc.)
And they're much less sneaky than Midworld predators.
In the second book set on Midworld (Mid-Flinx) the ecosystem actually takes out several spaceships that attempt to land; there's a natural fire suppression thing (exploding fire suppressant foam treetrunks) that is triggered by their exhaust.
Silverslith would probably be high Epic - low Legendary Tier; it seems roughly equivalent to a tarrasque, but somewhat bigger