We've seen both community developed Expansion Cards and other device makers starting to adopt Expansion Cards.
I can't imagine what other existing form factor would have been suitable and more useful than them just creating their own and open sourcing the design.
I'm trying to conceive of what other possible solution there could be?
Is there even such a thing as a standard dongle? Pretty sure there isn’t. And as you say you can just use the USBC module and continue using your USBC dongle. I bet you could even 3D print an enclosure to make sure that your existing dongle fits nicely into the module port so you don’t need the module.
And I don't think of or treat them like dongles - I don't carry spares around, I just have the configuration that makes sense for me. (I don't even have spares to change it, but with a holiday coming up I did think I'd swap one for an SD card reader if I had one.)