Have you ever in your life tried to use an angle grinder for this sort of thing? It’s one of a family of cutting tools built on the Ouija board principle. It transforms human energy into a crooked, unpredictable motion, and the more you attempt to influence its course, the more dismal your future becomes.

If i had a cast iron pan I had to flatten, I’d dog it down on my CNC router, set up a 1/4” endmill, whip up some code for 33% overlapping passes in Fusion 360, and take off .005” layers until it was flat.