Not a huge thing, but enough to break the page layout.
HTML relies just as much on your monitor's colour grading as PDF does.
(Your other arguments stand well enough.)
The render as I wish. ie are readable.
The reader can alter its format e.g. change font and the result still works. (agreed that it needs to be decent HTML - but plain HTML works it is some of the complexities that make this not work and I consider that a bad HTML page)
PDF is fixed format and you can't increase font size to make it more readable.
However for some of those use cases then not being able to alter PDFs is a benefit - e.g. invoices and bank statements but then you probably need more than a plain pdf which can be edited (e.g. change a 1 to a 9) but a pdf with some integrity checks.
Many times even things like page or column breaks are extremely intentional. Having something "beneath the fold" or flowing onto another page can drastically change the way someone interacts with the piece of media. No PDF isn't great (my particular beef is with how there's almost no sense of a sentence, block, paragraph etc so it makes it almost impossible to copy or parse for text), but keep in mind that HTML/CSS only just reached near-parity in features in the past 5-6 years.
I'm talking about documents which are purely valuable for their content, not for their branding, and where the reader's accessibility is more important than the creator's design.
Reading on an electronic device is a different problem than providing something to be printed on a fixed format unchangeable piece of paper.
Thus you have different formats for the two different requirements. The issue is people keep trying to mix them up.