All of that, plus a lack of understanding regarding the basics of astrophysics, it would seem. (e.g. I've seriously heard flat-earthers argue 'how can water stick to the surface of a ball?')
From what I've seen on youtube you're right, the one thing they all seem to have in common is that the have no understanding of gravity. Everything else seems to be an elaborate set of logical contortions to overcome this lack of understanding.