Strange WNR2200 did not work.
Ignore the power line adapters
Does laptop work in configuration below to verify WNR2200 is daisy chained to A7 router's LAN port ?
Internet === Archer A7 === WNR2200 === laptop ethernet
Make sure WNR2200 is set up to use DHCP for wan connection, and remember to change its LAN IP address (eg. 192.168.3.1)
Something else you can try?
reinstate the WNR2200 as your main router. Check power line speeds.
Turn on the Archer A7 (not connected to internet or anything else). See if power line speed through WNR2200 falls due to electrical interference from A7 or A7 power adapter when you turn the powerline adapters off and on.
Ensure WNR2200 and A7 use same AC mains power outlet.