I think it works, I remembered when installing the ONT the tech will plug in his laptop to test for connectivity and speed. However there no reason for direct connection unless you're doing troubleshooting since you'll need a router there to do DHCP and provide wireless wifi as I am sure you have more than one devices in your household. If you are thinking about using ONT as a "LAN switch" (since it has 4 ports), only the first port is enabled for 500Mbps/1Gbps plan and 1st/2nd port for your dual 1+1Gbps plan, the rest of the ports are disabled by default.
What could be possibly there is your machine running pfsense or hardware firewall that is running between your ONT and router filtering traffic first before it goes through your router.