I dabble in correcting other people’s spelling on occasion (can’t help it). Somewhat frustratingly, the usual reaction is “language evolves” and “everyone uses it this way” and “if it is understood, it does not matter how you wrote it”.

I agree with the argument that language evolves.

Still, "loose" is confusing because it makes me think for one second of the actual word "loose", so it breaks the cadence of reading (and thus it is not really "understood"). If the word "loose" didn't exist, I would have no problem with people misspelling "lose" in this way and eventually becoming mainstream.

Well only to a point, I don't think there's been any significant or formal "we spell this existing word like this now" in a very long time.

The only way English language really evolves now is by the addition / invention / adoption of a new word or added meaning to existing words, like yeet, influencer, youtuber, incel, looksmaxxer and simp. And a lot of them are meme words not actually used in normal parlance. Others are the wider adoption of subculture specific words and expressions, like AAVE getting adopted by teenagers / young adults.

I don't agree with those a lot. At some age, ones use of language stops/slows evolving I suppose.