Yep, I very much agree with this. It's probably inevitable that languages with reflection grow some kind of language-specific serialization format because a) they can and b) there's often some use case where it looks handy to have a format adapted to the quirks of the language. Plus, when some of these bespoke formats were created, the world hadn't converged as much as it has now around a few common text and binary formats.

But now the interoperable serialization formats have a lot more energy spent on tools and such, and the formats are better-specified, to the point that you probably want to use them even where interoperability with other stuff doesn't force it.