Correct.
My r7500v2 reserve partition has 3 ubifs volumes, 2 empty and one with data. In your PR you should mention that the r7500v1 and the r7500v2 are different in the respect that the r7500v1 apparently does not use its reserve partition. I suspect the r7800 is similar to the r7500v2
For other r7500v1 users that might want to verify that the "reserve" partition is empty "in place" (i.e. on the device without having to download a copy):
xxd is not available by default in openwrt but can be installed with:
opkg update
opkg install xxd
Alternatively, the dd/tr/wc commands are available by default and the command to run is:
dd if=/dev/mtd7 2>/dev/null | tr -d '\377' | wc -c
which should return 0 on an r7500v1
I can confirm a result of "0"
Did you ever get 5ghz wifi working ? I don't see this enabled yet in the OpenWRT 23.05.0-rc2 , was going to spend some time getting it working for a R7500v1 I have here.