Just a guess, but it seems like you work in theoretical lala land and never have to deliver something that works.
I'm not saying you are wrong- sure you can argue that it's the iPhone that is broken, from a non-standard format. However, if you are designing an app that needs pictures to be taken and about 45% of your customers (the students) can't just take a picture without going through some conversion while on a time sensitive test- then you majorly fucked up.
End of the day this is on the AP designers for not adding a format which 45% of their base will use by default.
Scanners almost universally output in TIFF, and need to be converted to JPG or something more universally accepted. Nobody complains.
Some scanners even will do the conversion to JPG for you, because they know nobody accepts TIFF files.
If Apple does it, then everyone has to accept it?
And why? Because images are large and Apple's trying to reduce the size on the phone? How about giving everyone more than 5GB of iCloud storage in 2020? Google gives you 10-15GB for free, and costs half as much for more storage.
Well I could turn that around and say if you develop a phone and the image format it exports to is not accepted by 99% of websites maybe then you majorly fucked up.
But the phone does the right thing when told to do the right thing. If the input tag has a proper accepts attribute set the iPhone will transparently and automatically transcode a HEIC image to JPEG.
A file input tag with no accepts attribute when you're expecting a particular type of file is broken. Would Android phones be "majorly fucked up" if they stored images as WebP by default?
HEIC isn't exactly a commonly used, or widely accepted image format outside of Apple's world.