I have a 3 unit Deco x55 system connected to a fiberoptic ONT at 600 Mbps speeds duplex

the main unit seems to be overloaded supporting the other 2 Deco x55's via wifi backhaul and the main unit enet ports connected to ONT, Windows 10 Laptop via enet gigabit port. and a Synology DS 220 NAS via gigablit enet.

I am considering buying a Deco x95 to setup as the Main and wifi backhaul 2 of the Deco x55's . in order to better maximise bandwidth throughput for my 3 windows laptops. BUT 

my android phones, and 2 Amazon Fire TV cubes work well (250 Mbps download) with great throughput but for some reason my laptops only get 10 to 40 Mbps download and 500+ Mbps upload via speedtest.(yes the upload is 10x faster than download) 

I  Do not know why, because when the laptops connect directly with the fiberoptic ONT they get the full duplex 600Mbps speed via speedtest. I am thinking that the 'overhead' of managing my 10 device network is too much for the main Deco x55 - Hence my thinking of using the much more robust Deco X95 as main is the way to go.

My question is : will the Deco X95 work as a main with 2 Deco X55's ?

I have spent several weeks working on this issue, even getting TP-Link to send me a whole newe Deco X55 system but no improvement. My last communication with Tech Support was to ask to elevate my issues to Deco Engineers