To be frank I don't give a rat's tail what the HTML looks like, I don't read HTML, I read what the author wrote. Nor am I a perfectionist, if there's the odd extra space here and there where it didn't oughta be, then I promise my sky wont fall in
Its only me and a few colleagues who read what I edit, btw I start with marked up text. My colleagues wouldn't know if they were run over by a truckload of HTML or were bombed by a mountain of CSS dropped from a Bezos drone (they'd probably prefer a ship full of CCS); so they too are unlikely to get their knickers in a knot about such things.
Roll on the day when the reader can configure all this stuff to what pleases their eyeballs, rather than being saddled with what others foist upon them.
I'll try replacing "non-breaking space" with "no-width non break' and a "1/4 em space" and see if I like what I see when a copy the EPUB to my Note.
BR