Let's not forget that Flash was the backbone of the ad industry back in the day as it was leveraged to produce rich media in the form of banners and interactive ads.
And now seemingly every site out there has dozens of popovers, subscribe to a mailing list (amazed those still exist and are somehow pushed more than ever), cookie permission requests, "Like and retweet us!" banners that slowly scroll from the side, "It looks like you could use some help" clippy style bullshit that choppily moves on screen, autoplaying videos that seem to autoplay no matter how many times you try to disable it and no matter how many times browser developers say "Okay, we finally blocked autoplaying videos for real this time!", 15 megabyte gifs littered throughout random articles just to catch your eye or to be hip and radical and show the writer is the bee's knees and knows what the kids like, scroll hijacking that only serves to make it choppy and physically painful to scroll, back button hijacking that involves filling your past 100 pages with the current page and sometimes getting caught in a refresh loop so it's impossible to move, endlessly loading bullshit content whenever you think you've scrolled to the bottom... I can go on.
Dealing with the modern web is like reading an infinite run-on sentence because it absolutely overwhelms you with shit and it doesn't let up. It's not hard to go to any random site and find 75% of the above all at once.
Flash was bad. Somehow web developers took its demise as a challenge to make the web worse.
Everything you said is correct. I also find it remarkable that the web has always performed like total dogshit, no matter how fast my computer has gotten. 20+ years ago it was in large part due to bandwidth constraints. Then 10-15 years ago that was essentially solved, but they continued piling more and more crap into the browser, and now it's a fucking app platform, and instead of clean efficient native software, we're now shoehorning every goddamn thing into the browser through layers and layers of frameworks, abstrations and "transpiling" or whatever.
I detest the modern web, and I find myself using it less and less.