I think you could argue the same for typewriter (monospace serif) fonts. Plenty of texts use them to denote the name of a variable or function in-line, much as we would use backticks to talk about `leftPad` here.
Though, as I understand it, the full-width characters are there not for any modern use cases, but for historical reasons having to deal with older character sets.
Still interesting.
A clean grid would be desirable in formal use, but formal use means trying to avoid Latin characters as much as possible. It's generally possible. Plaques and the like are much more likely to say e.g. δΊγδΊγεΉ΄ than to say 2020εΉ΄.
And I doubt you'd want to eliminate all formal uses of Latin characters. E.g. a plaque about a person would likely want to use their preferred name, which might be in Latin characters.
V A P O R W A V E
οΌ‘οΌ₯οΌ³οΌ΄οΌ¨οΌ₯οΌ΄οΌ©οΌ£
But, note that the identical process, much earlier, is how we got separate capital and lowercase forms. Writing systems never do that when they're developed.