@blaqkmage 

Hi, 
In your case, please provide the following information if you are willing to troubleshoot.

1. Please turn off the 2nd satellite Deco in an outside room, place a laptop close to the 2nd satellite Deco, connect it to the strongest Deco's SSID, then check the link speed and download speed on it.
You can turn off the 2.4GHz Wi-Fi and 5GHz Wi-Fi on the Deco app one by one to test the 5GHz and 2.4GHz link speed and download speed on the laptop. Then, please send us the speed test results.

You can refer to the instructions below to check the Wi-Fi link speed on your laptop, and visit www.speedtest.net to test your download speed.
What Is Wi-Fi Link Speed and How to Check It on Windows, Mac, and Android
 

2. "The far end device is also having issues showing the connected devices and uplink details in the app, so a lot of the time I can't even say what bands it's using for uplink. "
- Do you mean the client devices(such as phones and laptops) don't show the connected Deco and Wi-Fi band in the Deco app? Can you send us a picture showing this phenomenon?

3. Please send us the Deco app log.
How to Get and Send Deco App Log to TP-Link Support
 

Best Regards