The Archdruid is the Schroedinger's character in this story. It is completely up to the player, if after mission 2 he is there all the time with the heroes, or never there.
In the mission 7: Judging by their high levels, the troops assaulting Taslow's hut were the elite of SEAS, which makes it very clear, why is Babbitso mad at the Governor that he appears in person, no less than on his throne.
Even more likely, since the initial enemies were the urbanized Dust Raiders, who failed to stop the heroes.
James Warden might be the pilgrim the Governor is talking about, or at least the Paraworld natives might accept him as such.
Why do heroes in mission 12 travel with their tribal followers only? Could be because no army could be assembled in the peaceful Holy City on time, and besides, there was no urgent need for that.
SEAS fields sometimes more exo-suits and vehicles than infantry, which makes sense, because volunteers for one-way journey to Paraworld must be very rare and ground operators are needed probably just as a support. This would play well with the theory, that people of SEAS are actually mostly logistic, engineering and scientific staff and their units descriptions in-game are clearly from the heroes' perspective.
When we are at that, all enemies are called from the heroes' perspective.
The volcanic thruster engine would clearly not work the way it is implied by Ada. It might make sense, that both Ada was born in times before the books of Jules Verne, so she herself might not have any idea on this scenario and Cole who frequently displays Giving Up on Logic does not want to check if this world holds another nasty surprise.
Instead, Babbit's plan might be to just destroy the encroaching native armies.
Babbit is also a clear genius loner, so he must have been not quite socially happy even in his youth. On top of that, he is effectively the Last of His Kind, having outlived his generation by at least 50 years and seen both the rise and fall of the The British Empire, as he mentions in a diary log... and with Ada and Leighton being a quarter century younger than he is, he must feel truly Lonely at the Top. That is maybe, why does he truly trust only the two and is soHeartbroken by Adas betrayal, which left him only with Ax-Crazy Leighton. THEN everything he has built for at least 100 years starts crumbling