“Proprietary” might be a bit too strong of a word. But considering the tight tolerances of the framework dongles (to minimize damage), I would actually be more worried about plugging that into a different device and damaging the ports that way.
And I guess I still just think of that as a “trap”. Because the answer should not be “buy all your special dongles to customize your laptop” and more “usb c is fucking magic. Just get one dongle that gives all legacy ports you need”. Like, I am still INCREDIBLY wary of the data transfer so I have an old anker (irony) 20 buck dongle that I use on travel. But my old company made it a point to have a dedicated usb c dongle in every conference room and it was actually REALLY nice because you basically just plugged in your laptop and had a nice double display setup, keyboard, and mouse for every single meeting.