> and invisible symbols

Invisible symbols were in Unicode before Unicode was even a thing (ASCII already has a few). I also don't think emojis are the reason why devs add checks like in the OP, it's much more likely that they just don't want to deal with character encoding hell.

As much as devs like to hate on emojis, they're widely adopted in the real world. Emojis are the closest thing we have to a universal language. Having them in the character encoding standard ensures that they are really universal, and supported by every platform; a loss for everyone who's trying to count the number of glyphs in a string, but a win for everyone else.