. . .have physical access to the . . . ONT.

Doubt this is the case, but on the off chance that the ONT is configured to flow IP traffic over a coaxial cable attached to a CPE router (customer premise equipment), the configuration should be changed to deliver data over a Gigabit Ethernet directly to a good-quality GBE switch provided by you. New eight-port Netgears are surprisingly good managed switches for around $100. For under $600 you can purchase used 24-or-48-port Nortel/Avaya 5510/5520 switches on eBay. Though old, these enterprise grade switches have astounding performance characteristics due to the Broadcom silicon switch-fabric chipset. Were around $7000 new when they were current-gen. All above switches have VLAN support so one switch can operate as multiple isolated networks.

I run a Verizon FiOS 75/75 and the default setup is for Internet traffic to pass to a Verizon supplied Actiontec router over a coax cable.

Fortunately I hung out with the installer and found out up front--had it switched to the GBE from the outset.

For any VZ customers reading this, note that you can connect the Actiontec to your network so it can obtain TV programming information. The coax will continue to carry video and phone data which are on separate fiber optic wavelengths/channels.