That's incorrect, there's no guarantee uboot actually supports ping, since a different protocol, and the person who compiled it, might have disabled it.
Nor is ping needed for tftp recovery to work,
and isn't in any way a fool proof test of tftp functionality.
Rather the opposite.
Do you have access to GL.iNet GL-B1300 ? Matches all your requirement and can be easily recovered using built-in web recovery. No need to open it at all.
Ok if you have warranty then to recover the router go back to the store and say it stopped working. They will fix it for you, unless you already broke the warranty by flashing it...
Though its currently unavailable, it was a couple of weeks ago. Its top notch router, and I have been highly satisfied with it. Currently its my only router.
You can watch its review of openwrt on onemarcfifty's youtube channel.
I purchased it due to his review.
Xiaomi 4a Gigabit Edition router dualband with flashable EN25QX128A and GS25Q128 eeprom
easy to flash and easy to recover using ch341a usb spi nor flasher and lots of community support from https://4pda.to/forum/index.php?showtopic=988197 forums and also lots of custom firmware support padavan, openwrt, immortalwrt, xwrt,pcwrt and keeneetic firmware