You may as well make this argument against human speech. We need secure transport, not gibberish protocols.

Not really even a close metaphor, since human speech isn't a internet standard I could build devices against and sell to customers as compliant.

Considering that DPI devices are already sold to parse json-desribed protocols dynamically, I think you are a bit uninformed about my statement. It is not hypothetical.

Some DPI software also processes English, should we stop using it?

If you want security, you need encryption, not obscure encoding formats.