@Absolut 

Thanks to remind me that the Archer D7 is not included, we will add it later.

What is the speed you can get with your computer connected to the D7 by ethernet cable? 

Please test the wireless speed as well with computer connected to the TP-Link wifi only, and click here to verify the wireless negotiation speed. 

From the picture attached, the SNR margin value and rate data indicate there may have some issue related to the line stability provided by ISP. You can contact ISP to confirm it.

You can refer to the statement below. 

https://www.tp-link.com/support/faq/546/ 

Besides, here are some suggestions you can give it a go.

1. Ensure that the firmware is up to date

2. Customize the wireless settings to optimize its performance, including wireless channel and channel width. 

2.4GHz: channel 1, 6 or 11, channel width as 40MHz; 5GHz, channel 36, 40 or 44, channel width as 80MHz.

May it help, nice day.