After installing my new X570-I board, I noticed that the board is warped along one edge, as can be seen in the photos. Is this normal or acceptable?

That happened to me and i guess it happens to a lot of people. The problem its not motherboard, that happens because the case or either the graphics card aren't in perfect alignment. The IO plate of the graphics card can be adjusted to align perfectly to the motherboard, if its not aligned it can cause pressure on the motherboard witch happen to you, and also can cause bad connectivity between the GFX and the PCIe slot causing BSOD and all kinds of crashes.

I bought it from Newegg, do dealing with their RMA process would be a pain.

Honestly you cant't blame Asus for this, PCBs tend to bend over time due to various factors.