USB-C doesn't have to stay mandated. Once every single device and charger is using USB-C, they can let the law expire and the market will keep it a de-facto standard because no one is going to buy a phone that doesn't have USB-C unless it has a lot of advantages. Notice how micro-USB is no longer mandated in the EU?

Also USB-C isn't mandated the only port on the device. Add multiple charging ports. Plenty of laptops do that, even a few phones. It'll make the transition easier for people too because they can continue to use their USB-C chargers if they decide the new technology isn't a necessity. Just like how plenty of commenter here want to keep using Lightning cables.

The law has a reevaluation period of five years. Basically lawmakers and industry representatives will convene every five years to see if a new connector should be mandated. We already know that this works, because the entire industry excluding Apple had been doing it from the day the EU first told everyone to clean up their mess "or else".