1. remember to back-up or use iCloud. board level is not easy, and no benefit to repair unless for the valuable data inside. board level repairs always take shortcut and it will never as complete as the new one.
2. you don't understand the display screen component. you think you get cheap alternative, but in fact you purchased lower grade glass. Please do your google to understand what is the glass replacement for your phone OLED/LCD screen. For the battery replace, aside from lower grade battery pack, workmanship & repair job liability is the main cost.
1. I don’t want back up to iCloud, because I don’t want iCloud backup eat up my iCloud storage. Even if you backup everyday, there are chances you still have some valuable data didn’t get backup.
2. Lots of people who choose board level repair are desperate for their data. It never meant to be same as new one.
3. I understand there are different tire of screen. But if I have an iPhone 8, it makes no sense to spend 200 plus Canadian Dollars for screen replacement when the phone itself worth less than this. I rather take crappy screen so the phone function probably. This also true for older generation iPhone, like iPhone X.