Depends how you look at it. If I consider the amount of cables/charges/earpods we have as family this is logical move. We don’t upgrade all the devices every year but it still adds up. Most of them are just throwaway.
While people do have a million chargers lying around from over the years, almost none of them will work with the new iPhone. The average Apple enthusiast will still end up buying one or more separately.
The phone doesn’t care about the brick. It only cares about one end of the cable. All your old USB-A <-> lightning cables still work with their USB-A bricks.
It is my understanding that what you describe is not how charging works nowadays. For example, the new 15W MagSafe charger doesn't work at 15W if you plug it into any old brick. A particular charging profile (voltage and current) must be negotiated between and supported by both the charger and the device.
Every single brick I have had on an android phone for the last 10 years work on the iphone. The last 5 years of phones my family has got have come with usb C bricks too.
