Your frustration is understood.
When comparing the available iPhone self-repair options for iPhone - and your “independent” self repair of your iPad - you need to consider that Apple-supported iPhone self repair will use Apple-OEM parts and the necessary software tools to integrate and calibrate the replaced components.
By contrast, your own repair will:
a) not be using OEM parts. Apple does not supply original parts outside of its own network of Apple Authorised Service Providers (AASPs) or official repair partners - neither of which will supply these parts for retail.
b) not be using Apple’s software tools to integrate and calibrate the replacement screen - and reactivate the FaceID camera array (that incorporates a laser - that if disturbed, may not subsequently be eye-safe).
At this time, Apple supports self-repair of a limited range of iPhone models, Apple Mac and Apple displays. At this time, self repair of iPad is not available. You must use available genuine parts - and use the approved tooling.
I hope this clarification will help with understanding the substantial difference between a supported and independent self-repair. As you will hopefully understand, Apple will decline to offer support for unauthorised repair using components that are not of Apple origin.