The lack of ability to concretely define data structures is a huge pain, both when using it and when writing libraries to process it. You can throw JsonSchema at it, but now you have two problems. Can't use comments to try to work around that deficiency, even just to communicate intent to someone looking at an example record, at least not in vanilla json. Record streaming—basically necessary at anything resembling "scale", if you don't want to kill performance—is a non-standard afterthought in most of the ecosystem.

It wastes my time and tends, in practice, to cause bugs, all for no good reason.

I'd say "sucks" is accurate. Not that it's the only bad format we've come up with lately (YAML, ugh).