I agree that is a great feature and selling point for the Ioniq 5 and EV6. I also would like my Y to be able to charge that fast.
However, at least where I live (Central NY) and make long road trips, currently the public charging network is bad enough to completely eliminate that advantage. There are very few fast chargers and some locations only have 1 or 2 chargers. Not only do you need to hope they aren't being used but also need to hope they work as there wouldn't be any other options to charge. If a charging location even has a 350kW charger for the Ioniq 5 to take advantage of, there will only be 1.
When I tested out my CCS1 adapter last week at the nearby fast charger, there was an Ioniq 5 charging on the 350kw station, a bolt charging a 150kw station at only 30kw, and the other 150kw station wasn't working. Not very confident inspiring for long road trips.
I talked to the Ioniq 5 owner and did see that her car was charging very fast so I waited for her to finish. I used the same charger for my Model Y and it didn't charge nearly as fast as her Ioniq 5 but still worked very well. She did say on her trip from Buffalo that she experienced charging issues with the fast chargers being out of order and only 1-3 stations at each location. So a lot of waiting for a working station.
The public fast charging experience needs to improve a lot...I believe it will eventually, I hope.
