The problem with USB NICs is now you have two flaky failure points - the chipset driving the USB port and the chipset driving the USB network interface.
I had a reliability issues using a Realtek 2.5 Gbps USB network interface. Kept locking up, or having latency issues. Until I switched which USB port I plugged it into (one that used a different chipset), and after that it was solid.
Realtek itself (Questionable quality on a good day)
The implementation of Realtek by the ODM/OEM/SI into whatever part is being shipped, which given Realtek is the defacto "budget" option for networking, it's often done as cheaply and shoddily as possible, even if the chip itself actually isn't crapware.
And the USB interface as you point out. There's a whole rabbit hole that I'm unfortunately all too familiar with when it comes to diagnosing and dealing with USB. PCIe passthrough via a USB4/TB combo chip isn't as reliable as just using PCIe directly, but it's still better than a non-pcie passthrough usb interface.
They use the USB-C physical interface for their modules, but that doesn't mean they actually use the USB protocol on the backend. Not sure how they implement it to be honest, but it's at least entirely possible for example to run display-port only (With no USB involved at all) through a USB-C PHY (and dp isn't alone in being able to do that).
I had a reliability issues using a Realtek 2.5 Gbps USB network interface. Kept locking up, or having latency issues. Until I switched which USB port I plugged it into (one that used a different chipset), and after that it was solid.