- Well, it clearly depends more on your vision than your altitude, since half the time when a flat-Earther trots out a picture that *they say* still doesn't show any curvature even though it was taken at such-and-such altitude, I can clearly see curvature. If someone needs glasses as thick as Bubbles from Trailer Park Boys does, of course they won't be able to tell the difference between a slightly curved line and a straight one. And obviously at only 120,000 feet, i.e. about 0.5% the radius of the Earth, you're only going to see slight curvature at best.

 - Whatever explanation you have for how a ship on a flat Earth can be out of sight and come back into view with the help of a zoom lens, still applies for ships on a round Earth that just aren't over the horizon yet, so this argument is self-defeating and proves nothing.

 - Water doesn't find "level", it finds equilibrium, e.g. in a rotating water tank it flows to the edges and takes on a curved shape. This argument is just a new skin on the incredibly basic "it looks flat" argument that small children have when they're taught the shape of the Earth in school, and the new skin is "forgetting how water works", which makes it even dumber.