Fancy typography is the realm of magazines, not books, and I can't think of a single magazine that's stuck in my memory the way real books do. If you have to use fancy typography to make your text feel more interesting it probably isn't worth reading.
A surprising amount, actually. Mobile phones rezoom and reflow text and content automatically, and if you click reader mode, take over presentation entirely.
I don't agree with the idea that all CSS should be banned, but the pixel-perfect designs, that seem to come from Photoshop, are definitely annoying because they have rarely been tested on anything but what the designer had lying around. Have a device with a different scale factor? A phone with a non-iPhone screen ratio? Perhaps you dare use a browser that shows scroll bars by default? Good luck getting use out of any of those over-designed marketing websites.
I use tree style tabs so my computer has a 1920x1080 resolution, but not the entire width of the screen is available to websites. I've had to collapse the side panel repeatedly because some websites just couldn't deal with the idea that a desktop browser had a resolution that wasn't full width. I'll take on of those Motherfucking Websites over the marketing nonsense any time.
Except that the mobile browser does all that reflowing and resizing at the direction of CSS (its own fallback CSS in the absence of supplied applicable CSS).
Restricting CSS to any degree is in no way a solution here. What you really want is for people producing websites to bother understanding CSS and how to properly direct the design in a device-independent manner. Because CSS is fully capable of doing so at this point.
Mobile browsers do all kinds of special tricks that you need to manually disable. text-size-adjust is one of those properties that was added long after browsers artificially resized fonts to be larger than specified by CSS (and is still considered experimental from a standards point of view).
I wouldn't trust websites to apply my phone's font size the same way browsers do. Websites that do override the zoom factor often end up with huge fonts on my phone because I have the font size turned down (what's the point of a 6" slab of glass if you scale up the text so you get the same amount of information as on a 3" screen?).
I would estimate a percentage far closer to ZERO than even ONE percent.
Something like 20% of users use adblockers and that takes a fair amount of effort for regular folks. So, right off the bat, we're talking << 20% as a starting point because it's much harder than using an adblocker extension.
To be able to CREATE a user style sheet that can apply to arbitrary websites without making them look like ass would be very difficult. Unless, of course, one WANTS all websites to look like ass.
I guess, somewhere, there's a nice stash of ready-to-go css that folks can apply (using developer tools or an obscure extension) on their browsers? I don't know. I never looked. But that would involving a lot of fussing I can't imagine normal folks doing that at all.
Attempts to make sites "pixel perfect" is the worst habit from the print-world that designers brought online with them.