It's not a flat rectangle like you're imagining. Circumnavigation East to West is possible on both a plane and a sphere. North is at the center, South is away from center toward outer ring (Antarctica), and East/West are circles.

Beware of strawmen and other fallacious arguments, allow the opposition to be it's own representation.

The horizon is always at eye level, as it would be on a plane.
If we were on a sphere, the higher in elevation we went, the lower the horizon would get, to where we would have to be looking down to see the sky meet the ground.

When watching clouds/planes off in the distance, do we see them bending downward, showing us more of their underside as they went "over the curve," or do they stay level and seem to get closer to horizon as they reach the limits of our perception?

There's tons of evidence. [They] convinced us that our own senses deceive us, and we must trust what they tell us reality is, as they've done with everything since. A wizard