> If a thumbs up with a different skin tone is a different character

Is it? The skin tone modifier is serving the same purpose as a variant selector for the CJK codepoint would be.

The underlying implementation mechanism is not the issue. If unicode had actual support for Japanese characters so that when one e.g. converted text from Shift-JIS (in the default, supported way) one could be confident that one's characters would not change into different characters, I wouldn't be complaining, whether the implementation mechanism involved variant selectors or otherwise.