Which arguments that i made against RM have been weak in your opinion?
The only 2 I've seen you offer. The apparent change in the circumference of the sun if the claims of flat Earth are true, and eclipses.
You are right of course, but both are very weak arguments.
The best way to beat a flat Earther, is to find a scientific principle he agrees is true, like for example, why droplets and bubbles are spheres...
As a planet gets massive enough, internal heating takes over and the planet behaves like a fluid. Gravity then pulls all of the material towards the center of mass (or core). Because all points on the surface of a sphere are an equal distance from the center of mass, planets eventually settle on a spherical shape.
And then have him explain a flat Earth claim that contradicts the very scientific principle he has agreed is true.
He defeats himself.