Stuff that would be smaller, tighter, faster, and less code without the library, NOT counting the size of the library against the total...
Things that have ZERO business on a website in the first place and only piss on accessibility from orbit or outright frustrate users.
Semantic markup and CSS's job.
If you remove jQuery from the equation, the latter two still apply on probably over 90% of what people do with it, at least for conventional websites. Web crapplications that will standalone outside a normal browser are a different story, but for websites where you might actually care about usability, accessibility, and graceful degradation, SO much of what people waste their time on with scripttardery is just telling large swaths of users to go plow themselves!
Much the same can be said about most anything client-side with the word "framework" attached to it, and for the most part I say that about server-side frameworks too. They result in being more to learn, more overhead, writing more code that's more convoluted... then the people who advocate the use of such things make wild claims about it being magically somehow "easier"? The only way I can have that make any sense in my mind is that such folks generally don't know enough about HTML, CSS, emissive colourspace, accessibility minimums, etc, etc, to even be flapping their gums on the topic.
Hence why if you press them about the WCAG, they either go "what's that?!?" in ignorance, or instantly on the offensive because it's "too limiting" to them as an "artist".
Art is only a small part of design, sadly too many artists and scripting junkies under the DELUSION that they are "designers" lose sight of that -- which is why there are so many websites out there that while very pretty, are the accessibility and usability equivalent of those "death ray" buildings that keep cropping up around the globe.
I have a rather ugly and insulting rant on the topic on my site, it's something of a pet peeve watching all these halfwits vomit up a megabyte or more code to do 48k or less' job... more so when it's all blind copypasta and they don't even understand how any of it actually works... hence their being utterly and completely lost when the fat bloated rubbish breaks.
Don't even get me STARTED about mouth-breathing halfwit re-re idiocy like bootcrap.
Ditto, your rant has merit!
I'm more of a front-end web designer; my skill set is more like a swiss army knife… (a hack of all trades; but a master of none).
I find bootstrap too overly complex & bloated. I like simple & lean css frameworks.