I'm a huge fan of Readability Mode and use it often. It's proof that Web design isn't the solution, Web design is the problem. For those who are using e-ink devices, or even just standard tablets, EInkBro is another immensely useful tool. Yes, it's a standalone browser, not a mode on Firefox, Safari, Vivalti, etc. https://github.com/plateaukao/browser (Available through Google Play, F-Droid and other sources. Android…
I wish somebody would create a DL/GAN/style-transfer tool to automatically change the style of any website into https://motherfuckingwebsite.com/ (regardless of how the website is structured, so deleting the CSS doesn't count)
For some web pages, deleting the CSS can help, sometimes not. Perhaps the way to go about such a thing is to consider mainly HTML, also considering CSS and ARIA to fix the layout (some web pages have forms that don't work correctly when CSS is disabled, but I have seen them have ARIA; an implementation could use ARIA to fix up any forms that are broken by doing so). So, while the CSS can be deleted, it still might need to consider it for some purposes, such as checking if something should be removed or formatted differently (e.g. emphasis, fixpitch, etc; HTML can specify such things too but it is not always done properly).
(That web page does have Google Analytics, with the comment "yes, I know...wanna fight about it?" preceding it, but you can just disable JavaScripts to avoid it.)