Yes, but the round earther can provide a model that matches your observations. Round earth is a better model because it matches reality more often while also accounting for a lot of the obvious flat earth arguments (mostly, that they hold true locally).
But they don't care. And more importantly, don't want to agree with you.
Then it's not persuasion in good faith.
Of course. Good faith is pretty rare and subject to, shall we say, hostile evolutionary pressure in online and public policy spaces.