No, you can't always do that. We have workarounds for platform bugs that were even fixed, because we get users with old devices that can't upgrade. You cannot fork a phone of a random person on the other side of the world. Once a platform bug is out, it can stay out in the wild for a very long time.
Our website codebase contains a workaround for a bug in native Android file picker in Samsung One UI. How are you supposed to solve this by "deploying your own platform?"
So, when operating system gives you invalid file, it magically becomes valid, because your UI code is in a different file. Sure, that sounds plausible.
If you have the spare time, you can try and submit your patches upstream; in the meantime, you just maintain your own version.