That was my take on it, too.
I'm happy to say my 15 years of experience in information systems didn't lead me wrong: the problem was, like I suspected, not my equipment.
After a couple chats with Verizon, they sent reset commands to the ONT and confirmed the provisioned speed, they also send some telcom magic to the equipment down at the demarc.
Suddenly, a laptop connected by CAT6a to the ONT could pull 900Mbps down and over 800Mbps up on Verizon's speed test and very nearly the same thing down on fast.com.
To think, if I'd been a less tech savvy customer, they'd have probably convinced me to go back to using that buggy G1100.