Defence strength of available divisions is 94.1746. Required strength to force a surrender is 1047.
Aye, that's fairly average.
What. The. Hell. That's more combat strength than my empires entire ground army by a factor of 4.
Then your army's too small. I don't mean to be facetious; conquering a populated world takes a significant number of troops.
It'd take YEAARS to train up enough divisions to do that.
Yes, which is why you should be training new ground units non-stop from the moment you start Aurora. Especially since those conquering troops will need to stay on the ground for
years as an occupying force, so they won't be available to conquer anywhere else for a few decades.
Is this normal?
Yes.
Is this sensible?
Yes, though Steve has 'revisit ground combat & occupation' on his to-do list for a future version. Feel free to lobby for any changes you wish to see.
Is there a way to make them capitulate quicker than taking years to train up and deploy millions of my ground warriors to the planet?
Warships overhead give a bonus to the surrender roll, as do demonstration nuclear strikes. Chuck enough missiles at them and they'll surrender - once the planet has become uninhabitable. #:-[