Argument can be made if your camera doesn’t support 4k or 60fps, there’s very little need for higher speeds than USB2.0 since files generated won’t be as big. However if you keep using your phone as a camera to record long videos, then yes it’s annoying to have slower interface.
That’s a valid point.
Also is there’s a USB3 controller at all in the phone to connect the camera inside the phone? Or does the camera talk on a different bus on the SoC?
With Apple devices I honestly don’t know. With others SoC is the one exposing the rest of the hardware and acts are intermediate. Historically in general giving DMA access to any hardware on the system has proven fatal when it comes to security. You do gain speed, but expose so much in the process.