Once you start taxatively naming "these are the Only Blessed Ranges," you'll be bitten by the usual brouhaha "email address ends with .[a-z]{2,3}". We all know how it went, and ".[a-z]{2,4}" didn't cut it, either, not even in 2000.
Why? How do you come to this conclusion?
Think of it as though Unicode decided that the letter "m" wasn't needed to write English text, since you can just write "rn" and it'll be close enough. Someone named "James" might want to have their name spelled correctly instead of "Jarnes", but that wouldn't be possible. Han unification did essentially this.
Prove me wrong with a counter-example.
First search result.
Both character fall into the first category I mentioned, no variants.
Note that GP claimed "not representable" (not "not represented"). Based on what I know, that claim feels quite wrong.