Latex works fine but is far from perfect. People use it for lack of better options, but it's not exactly a joy to use (not for me at least). After 35 years, surely we can expect something better. So thanks to those working on that!

I'd say the problem isn't so much about readability but about ease of doing certain things. Case in point: non trivial tables, with multirows/multicols, newlines inside cells, and so on

But aren't hard things going to be hard to do?

There are things that, if you did them in a GUI, would be multiple steps down the tree of menus. It seems natural to me that they require multiple commands.

(Not that LaTeX is perfect, for sure. Admit I only glanced at this. But after trying a bunch of things that the author asserts are simplifiers, I've not found one that is as capable. All too often they make super simple things that are already simple, and then fall back to LaTeX for the rest.)

Debugging those tables is still a pain in the ass. I am certain that we there's a better way than today, where if you accidentally add or remove a newline your table breaks

(Disclosure: Not an expert.) Standard LaTeX, meaning what exactly? Since 1983 there's been LaTeX2, LaTeX2e, and amsmath and the hundreds of packages that are now standard. The LaTeX used nowadays is a lot of stuff built on top of the improved later versions of LateX, which itself was built on top of Plain Tex (itself built on Tex).

I love how LaTeX/TeX is completely programmable, and anything particularly unreadable/messy can be made readable with user-defined commands, environments etc.

Have you tried debugging LateX? Miss a comma somewhere or screw up a package's options, and you'll be left wondering why your paper is broken, and then you're at the mercy of Google to help you find another person with the same issue.

LaTeX produces beautiful papers, but it's old and showing signs of its age.

Is it that bad? Have you tried to debug Markdown + LaTeX MathJax? Is it the same of differs? As for me it seems enough easy to debug each single math object. But I only used Markdown + LaTeX insertions so I cannot compare.

I've written papers with some complex tables, probably over 150 pages worth of dense latex, and I still have trouble debugging :/

I wrote my thesis using latex, and can with confidence say, no, it is not "working fine".

Maybe in the sense that COBOL is "working fine", so we should all just stick to that too.

But LaTeX itself was (and still is) just a wrapper on top of pure Knuth TeX to make it seem more like a once popular markup language called Scribe.