Sure, if you make up numbers, you can argue that the sun is going to crash into the earth tomorrow and we're all going to die, so nothing in this conversation matters.
In reality however, there are some cases where protobufs, flatbuffers, or BSON are superior to JSON, but there are a lot of cases where they aren't. You'll have to weigh the pros and cons for each situation. And a lot of the time, there's not time to benchmark everything, so you kind of have to guess how the elements of the system are going to interact.
The one element that every system has is humans, so it's a fairly safe bet that humans will have to read whatever format you use.
I spend probably 15-45 minutes a day just in Postman, testing JSON calls. If something goes wrong, I'm inspecting requests/responses in Chrome. When we integrate a new team member, we don't have to have them install any tools--they're included in the browser they have installed. We don't have to write any schemas. When I start a new project, I don't have to install any libraries: they're included in my language(s). When we integrate with a partner company, we hand them sample requests/responses as text.
How many JSON documents per day do we have to send to get the payoffs you're claiming?
And my company is not unique: in fact, the stack I'm using is one of the most common stacks on the market.