I was just reading through the wiki page. The specific install notes given for the v2 indicate that if you are running stock, you need to flash another firmware that will pass TP-Link verification first, and it links to a DD-WRT image. OK, fine. But then step 2 goes into flashing an old TP-Link firmware that doesn't do image verification before going on to step 3 (flash OpenWRT image).
I'm left wondering, why? Can't I flash the newest OpenWRT from the old DD-WRT install? Why is an intermediate flash of an old TP-Link firmware necessary?
While many years since I went from OEM to OpenWrt, iirc it was simply a matter of using the correctly qualified factory image (us, eu, il). Certainly did not do any of the steps on that page (ddwrt); may have been OEM FW version dependent though.
Some of the newer Archer C7 units may need some funky ways around "signing", but I don't recall any issue with any of my v2 units. If you have any problems, tftp install has been 100% for me over the years.
It's generally a bad idea to trust anything but OEM firmware to be able to flash a "factory" upgrade, or, unless you have good knowledge of the device, to trust anything other than OpenWrt to be able to flash a "sysupgrade" image.
Different kernels may have a different notion of how to divide up the flash memory. If not compatible, it may write the image to the wrong place, potentially destroying important, device-specific data.