I'll add to this that I find if you're willing to get really zoomed in with it, this issue can be mitigated. For example, with low frequency vocal bleed, I have found that the offending sound is not usually right ON the bass guitar, but just a few hz above or below it, like at 290 rather than 300, you'll see a little deeper colour jagging off the flush note at 300. Removing those jagged edges tends to clean up the sound completely. Might there be some bass trapped in there too? Possibly, but it is not what I would call audible compared to the significant change in the vocal portion.

On the other end, if a hard consonant sound is left in the mix, at a high frequency, particularly when there is no cymbal in that area, there is little to no sound to conflict with it at 15kHz. Now yes, the 'air; is important. Without it you get this muted dip, but the vocal artifact will in those cases sit as its own blob of colour surrounded by the faint non-colour air. Just digging in at a really high zoom level and bringing that back so it's all level generally makes it all sound smooth while retaining the air. .. as opposed to just hacking it out in one big clump.

The same kind of philosophy can be applied to middle ranges. If there's a sharp artifact sound, bringing the heavier blob of colour down to blend with the colours around it is generally effective. There may be other instrumentation in that blob, yes, but if the volumes are equal around that space so the shape looks like it should, then I find it does sound as it should.

I mean, I don't want to take the organic nature of sound out of it and be totally mechanical, but like, the spectrum is just a digital representation of what was played. Every frequency is a note, and the different volumes of those frequencies blended together is what gives those notes the sound of being guitar, or a trumpet, or a voice. There's no way to ever be 100% accurate, like if you repaint a painting it'll never be 100% the same as the original, but you can try to be as close as possible to it. And I think that while that may not be enough for circumstances where only total purity will do, there is a matter of weighing at what point the difference becomes so undetectable that people just won't care in the context of what you're using it for.

I totally struggle with this. I mean, I get waaayyy too fine with my work a lot of the time, when my friend just skips the 10 hours of fiddling, posts the track, and everyone still loves it just as much.