The problem is not backward compatibility but labeling. A USB-C cable looks universal but isn’t. Some of them just charge, some do data, some do PD, some give you access to high speed. But there is no way to know.
I believe the problem here is that you will have PNG images that “look” like you can open them but can’t.
Cable labeling could fix 99% of the issues with USB-C compat. The solution should never be blaming consumer for buying the wrong cable. Crappy two-wire charge-only cables are perfectly fine for something like a night desk lamp. Keep the poor cables, they are okay, just tell me if that's the case.
the parent said "changing the compression algorithm will break backwards compatibility", which i assume is something works now won't work in the future. The usb-c spec is intentionally trying to avoid that.
Some aren't even USB. Thunderbolt and DisplayPort both use USB-C too.
That's not just an issue with usb-c. normal usb a and b cables can have data or no data depending on how stingy the company wants to be, and you can't know until you test it