I test at this time:
XIAOMI R3G mode AP WDS
Cyberoam CR35Wing STA WDS ( with relayd or without relayd )
Internet fiber 2 GB/s Orange Livebox 6 < --LAN gigabits --> OpenWrt XIAOMI R3G MT7321 < -- WIFI 5GHz --> OpenWrt Cyberoam CR25 MT 7612 < -- LAN gigabits --> Computer
I have some 300 / 200 Mb/s
--
Internet fiber 2 GB/s Livebox 6 <-- WIFI 5Ghz --> Repeater Orange Wifi AC <-- LAN gigabits --> Computer
I have 650 / 500 Mb/s
--
Where do you think the difference would come from ?
wifi5 vs wifi6 (livebox6) 
The more devices, the worse.
A true comparison would try to have a stable setting and then to only change ONE thing. This also entails to not change the location of your devices.
Hency, try to compare like this:
I would also recommend the usage of Iperf3 to speedtest your local network.
The Orange repeater is the old model ( not Wifi 6 new repeater ) with only 5 Ghz
*
1 - I use for examples A & B 2 * OpenWrt boxes in relay mode to pass Orange TV
It works not too badly in these two cases except for the flow
I have DLNA, Samba...
It is also practical because I have 5 LAN ports available.
But you need two OpenWRT boxes
2 -- With only the Orange repeater the speed is very good except that i only have two LAN ports available & no TV problem
3 - I cannot use Livebox 6 < --WIFI 5Ghz > OpenWRT <- LAN > Computer + Orange TV UHF because Orange TV does not work
4 - I ordered a ASRock G10 Gaming Router + H2R box
I will compare the original firmware and OpenWRT to see this speed story and also TV compatibility
