Can I reduce the cornmeal in this cake without adding anything else? I'm worried that it will be too dry. Also, would oat and almond flour work as a s

Also, if you want to make this a GF cake, cobbler or crisp, there are recipes out there that have been tried and refined many times.
Maybe look at some of those and see which you prefer.

I think either would probably work, but I wouldn’t just cut down the cornmeal unless you want to turn this into a two layer cake. One of the reviewers did think the cake was dry. Another recommended increasing the peaches or you might not have enough for the showstopper appearance in the photo, so I’d probably prep 4 or 5 peaches depending on their size— you can always snack on them if you have too many.