That's not correct and very misleading. The wattage is the max amount of power the charger can output. It's up to the device being charged to negotiate and pull the right amount of current and wattage. This is case with modern charging protocols and even older 5v usb chargers. This is similar to how you might have a 15A rated outlet in your house, but that doesn't mean it's going to "force" 15A though whatever device you plug into that. It's the device that determines how much power it will pull.
My analogy is an EV - of course your EV isn't going to pull current that's dangerous but fast charging it has been shown to degrade battery life - especially if the EV doesn't have active cooling for the battery pack.
Putting that EV on a slow charge that might be sufficient for an overnight charge might be better for the battery pack.
This is a setting on the device side. The EV it self will decide how much current to pull, based on charging profile that you set.
You are correct on that charging at higher currents can reduce battery cycle life, but it's the device it self that decides how much current to pull based on the charging profile that you selected. In your example with an EV,you set the charging profile on your vehicle, not the outside charger. The charger's job is to provide as much current/voltage as requested by the device.
It is just plain inaccurate to state that GaN is the problem, or opens up new possibilities for fast charging. All it does is make the charger smaller.
