A browser and its privacy is much more than the engine. You could take webkit and make the most spying browser ever out of it. Most of what Safari does for privacy resides outside the engine itself.
Ok looked it up: Steam switched to CEF in 2010 (announcement read „WebKit based“), CEF3 with Blink was considered stable and recommended in 2013. So they probably used a WebKit base for at least these three years. But, unless they still use CEF1, it’s not WebKit anymore today.
The engine is HTML. No more is needed to give me the information I want, though CSS and images are certainly nice. JS would be more like the infotainment system: Sometimes nice, sometimes annoying, sometimes dangerous.
To say it the other way round: Use HTML/CSS for information purposes (JS where needed, nice explanatory animations etc), get back to using real nice native code for applications, using the OSes capabilities to the fullest, providing an experience integrated with the rest of the OS, having full performance.
You can export whole projects as one-file markdown (or HTML, RTF), worst case being having to go through every project, exporting and splitting the file up (by a script), or turn the agenda folder somewhere in ~/Library (contains bunch of json) into something usable via script, but I agree, it lacks a reasonable solution for getting it all out at once.