I'm an owner of an Archer C7 v2 with serial number starts with 2169 and it works perfectly fine on LEDE-17.01-rc2.
As for TFTP, maybe you need to flash an up-to-date stock firmware to update U-Boot, which contains the TFTP recovery procedure. LEDE doesn't include the U-Boot partition. Beware that newer stock firmwares might me region locked; you would then have to use the LEDE image that contains the appropriate region.