Hello @AhmetB 

Speed goes into AV600 will be capped under 100Mbps,  because  network interface is of 100Mbps (Fast Ethernet port).

And speed will again get reduced when signal  travels through the house powerline, Here is a  FAQ explaining the Powerline Rate and Actual speed of the Powerline Adapters: 
https://www.tp-link.com/support/faq/2928/

For WPA4220, speed around 60-70Mbps could be reasonable as in the real house environment the speed is around 20%-35% of the powerline rate, also limited by the speed comes into the powerline unit. You may try a higher WiFi Channel width 40Mhz from web UI and see if speed improves a bit. 

May I know the country version (Eu, UK, US etc,) of on the sticker of the powerline unit, please note the country version hardware version before download firmware.

https://www.tp-link.com/support/download/tl-wpa4220/#Firmware