The questions about readability when things go wrong. When binary data breaks, mostly your just screwed in figuring out went wrong, especially when it causes your decoder to fall over. When ASCII data breaks often a view of the data can point at something even when tools can't.
Reading a binary file is no different than reading ascii. I experimented with writing a debugger, which meant learning how to parse executable ELF binaries. It really wasn't bad at all. It just takes a bit more time to figure out what the bytes/data are expect at what offsets. The real un-said reason is a) programmers are lazy b) its easier/cheaper to hire people who can read ascii than find someone who is a bit more experienced and can figure out how to debug binary parsing.
Yeah and to b, it really just comes down to a lack of tools and people experienced in those tools (IMO).
There's no reason a binary format couldn't be as easy to read as a JSON format. All you'd really need is a "binary->json" gui and you're off.
It would take a little effort to make such a tool and you could have it integrated into every browser.
It's not like something like that is unprecedented even, After all, there's no browser tool out there that's showing you the gzipped resource on a compressed endpoint. It's always already doing the step of gunzipping. binary->Json would similarly be just an additional step the browser could do in the tools.
You are almost certainly passing these through tools (even built into the browser) that are doing extra processing to make it more readable.
Let's assume, for example, CBOR ends up taking over JSON. Do you not think browsers wouldn't have a CBOR parser to make it more readable?
This isn't bolt vs welding, this is bolt vs bolt with a washer. Yes there's a small extra step, but not some sort of insurmountable hurdle.