“I believe Apple will optimize the fast charging performance of MFi-certified chargers for the iPhone 15”
They should. MFI is a highly test controlled standard that guarantees safe operations with your iPhone. But why does Apple do that? Because that is what Apple does, they make a product that is curated and has specific tested interoperability.
To many consumers a cable and charging brick all look the same. Apple makes it simple to know you’re getting the best standard. That’s what Apple does and offers. If a consumer doesn’t like that approach then go buy an Android.
Live simple but smart, buy MFI. Yet live even simpler and smart, buy MagSafe 😀