The duplication there is mostly to remain compatible or trivially transformable with existing encodings. Ironically, the two versions of your example "A" do look different on my device (Android), with a slightly lower x-height for the Cyrillic version.

The irony is you calling it irony. CJK "the same or trivially derived" characters are nowhere close to that yet given same code points. CJK unified ideographs is just broken.