EX6150/AC1200 Dual Band - Slow Data

My home internet promised speed is 450Mb/s, I usually see around 400Mb/s on my main network.  I use a MacBook Pro, running latest MacOS.

With the EX6150/AC1200 extender I see 4-10 MB/s on the 2.4 Ghz channel and 20 MB/s on the 5 Ghz.  

I would expect a decrease across a WiFi extender, which is why I bought one with 1.2Gb/s throughput.  Yet I am not seeing anything near this.

Any ideas?