100% due to the crappy hubs.

I have a gigabit connection and have been using the CalDigit TS3+ since it came out. Zero issues, zero problems with it stepping down to 100 Mbps or anything else. I have GigE plugged in, two monitors, two large disk arrays, sound, and usually a couple other random things. The monitors and all peripherals work flawlessly, wake flawlessly from sleep, etc.

Every time I test the speed, it's around 940 Mbps, which is about the max that a gig fiber connection can actually push to you. Every time.

By contrast, a lot of my IT clients have tried to get by with the crappy cheap USB-C hubs or docks mentioned in this article, and without exception, they always completely suck. Eventually, they start listening to me and they buy a quality dock instead, and then their problems magically cease.

Potentially, but the problem is that now you had no choice. Back then, your laptop would come with a reputable (most likely Intel) Ethernet controller that you would use so you had no reason to buy an external one and bear the risk of getting a shitty one. Now, more and more laptops don't have an Ethernet controller, so you have no choice but to roll the dice and churn through multiple dongles until you get one with a controller that doesn't suck.

A good NIC doesn't have any of those issues. It all comes down to their poor choices in what ethernet IC to use.