Key phrase "They never actually claim this browser is working and functional " This is what most AI "successes" turn out to be when you apply even a modicum of scrutiny.
No you see you just need to prompt it to implement functional and working code. You're just inexperienced and holding it wrong
In my personal experience, Codex and Claude Code are definitively capable tools when used in certain ways.
What Cursor did with their blogpost seems intentionally and outright misleading, since I'm not able to even run the thing. With Codex/Claude Codex it's relatively easy to download it and run it to try for yourself.