What they said does make sense though. I build a very small parlor guitar that has a dead flat top and I have built guitars as big as an L2 that had flat tops too. In either case string tension does indeed pull an arch into it. But arching the top is good for protecting it against rapid changes in RH so there's that.
I don't use a radius dish either but I do radius the braces and then simply use flat flexible cauls on the back. If you tape them in place it helps.
https://www.tiktok.com/@piusone/vide...81200673441285