By "client" I mean the unhackable blob of minified js which is the one and only piece of code in existence that knows how to get any useful content out of today

By "client" I mean the unhackable blob of minified js which is the one and only piece of code in existence that knows how to get any useful content out of today's revision of one server's undocumented protocol. APIs are the problem, they are displacing portions of the web which were far more reusable. They require custom clients (usually in js) per site, and the authors who aren't responsible enough to do progressive enhancement are the same ones who aren't capable of (or even interested in) maintaining a documented, stable, backward-compatible API for years. Markup changed but was at least mostly self-describing before it became acceptable to serve obfuscated data and repair it using code that end users shouldn't need and oughtn't blindly trust.