@Cylac 

There is not much you can do with configuration settings when Deco runs in Access Point mode, and when it runs in router mode whatever you try in configuration would not improve AP speeds but could make it even worse.

You have done multiple correct speed tests, but if you haven't tried it yet, disable 2.4GHz in Deco mesh to force wireless device stay on 5GHz all the time, and rerun speed tests with only Main Deco up.

The best I've ever got from M5 (which is similar hardware and specs as M4) was 450Mbps, with most speedtests giving results in the range of 300-400Mpbs.

Tested with Android smartphone, Deco runs in AP mode, M5 is wired to the ISP router, only 5GHz enabled, very little interference from other networks. Using fast.com, speedtest.net, Android speedtest app, Ubiquiti WiFi analyzer speed test.

By the way, when you check wireless client WiFi link speed on iPhone, what does it show? If you need instructions how to check that, see TP-Link FAQ article How to check the associated/link speed on a wireless client.

If everything done right, you should see 866Mbps there.

@Alexandre. Thanks for replying!

yeah all my connection speeds have been verified. 

i also reconnect my wifi when I'm next to one of the Deco pods to ensure I get a 5ghz connection. 
 

I'm pretty sure my channels are saturated.. however I can't switch the channel on these things.. which is frustrating. Rebooting doesn't auto-correct this problem either. 

I've been using TP-Link devices for years (modem/router/switch/smarthome devices/etc) and so for I've been very underwhelmed by these Deco devices.