If you use CableMatters Ethernet adapter, and have steady speed limits in the 90’s

I have a question for you. Hello, all

Recently I got the $18 adapter from cablematters, and I guess I was expecting higher speeds. On a PC, I get speeds in the 300’s, IIRC (without that adapter, of course). I have unlimited internet plan, and a tp link 1G internet switch between the modem/router and everything I connect to the internet by Ethernet . Using a Cat6e Ethernet cable between the Firestick 4k max latest gen, and the switch. Pretty sure it’s Cat5, or Cat5e to the router/modem, from the switch.

Just wondering if any of you who are/were in the same boat as me, have found a solution for the steady speed limit in the 90’s.

Thank you for your time.