e.g. the device might charge with USB C but they’ll gimp the data transfer rates on non-pro phones.

Just so you know, there are others who have slow speed on USB Type-C already. My mother's Galaxy A52 has a USB Type-C port that has only USB 2.0 support for data transfer, but with USB PD 3.0 PPS charging up to 25 W.

To me it's legitimate to use USB Type-C for better power delivery even if the chipset runs only at USB 2.0 speeds for data transfer. But hobbling a fast chipset just for product segmentation would be shitty. It is something I could see Apple doing though.