Deco S4

If you actually read through the page you linked to, you will find out that Deco S4 runs on a Qualcomm Atheros QCA9563 processor (single core, 750 MHz) with 128 MB RAM and 16 MB storage. These are minimum recommended specifications for OpenWrt (in other words, Deco S4 is a very basic device). As is,

Consumer-grade equipment often can't handle dozens of wireless clients efficiently. Assuming that your setup is like this: Bridged ISP > Primary S4 > Switch > The rest of your stuff . . . then you should be seeing decent wired speeds. If you get 1GB speeds when directly connected to your ISP's route

...opnsense which I believe to be a OS for your router but while looking into it more I found someone saying it runs on a computer and not on your router. Both OPNsense and pfSense actually are "distributions" (somewhat like Linux distributions) rather than OSs themselves. Both run on FreeBSD, which