Winston Churchill wrote:
Your arguments basically went from 'it's not an issue at all' to 'who cares about the minority of people who are experiencing the issue'.
I haven't changed my mind at all, it's not a known issue and I didn't say I didn't care what the minority want, but just because you or somebody else wants something different (in any numbers) doesn't make it a known issue. If everything that somebody felt should be done differently was a known issue, everything or very close to everything would be a known issue.
I'd like to be able to share photo albums in Photos at full resolution with chosen recipients, that doesn't make the fact that Photos doesn't do that a known issue nor does the fact that I might be in a small minority mean I don't care.
That Photos analogy would be like saying you'd like to be able to get a Tesla Model S with a 500 mile range and the fact that you can’t - because the specs max out at 335 miles - shouldn't be considered an issue, in which case you would be completely right. But that's not at all akin to what's going on here.
What's going here would be more like getting car and finding out that the driver's door opens slightly, but noticeably, less than the other doors. Not because it's broken, but because it was designed that way, for whatever technical reason. Regardless of what percentage of users would actually be bother by it, we would all agree that it shouldn't be designed that way because for a car manufacturer it shouldn't take magic to design a car with all of its doors being able to open fully.
An Apple ID's name can be changed to any third party email address but not to the iCloud email address that is associated with it. No matter how you spin it, from an average user's perspective that doesn't make any sense and - instantly and intuitively - feels wrong when encountered. Some may be bothered by it, others may not. All who encounter it will however consider it an issue in the normal sense of the word because it should just work as would reasonably be expected - and it doesn't. It's the software equivalent of the driver's door that opens slightly, but noticeably, less than the other doors.
It's arguably worse that it's not just a bug because it means that the design, in this regard, is inherently counter intuitive.