If you would recreate WordPress from zero, what would you change?

I'll start. I would create subheadings in the left panel named after the team responsible for that part of the website. E.g. Marketing, Design, Legal, etc.

Rethink Gutenberg. The entire system is built in php, but this aspect requires you to know react, et al to extend it? That doesn't make a lot of sense. I love the block-based building pattern, but I shouldn't need to rely on something like ACF Pro to create my own blocks without going through the pain of learning a new stack.