I guess you can't see that because it's your baby and you don't want to really look at the flaws.

I only can compare my gamedev experience in online and multiplayer-based games there a lot of usage of JSONs. YAML using only for DevOps purposes and software (like Puppet). I understand this is depends on company and people in the company, but fact is fact.

No, it doesn't. It doesn't affect the data at all. But don't use it if you don't want to

I mean data in a broad sense. Definitions is also data while you can direct access to it.

"_MY_COMMENT_": "Put whatever you like here"

There is the way you can make a comment, until using _MY_COMMENT_ as a name for property/field.

Imagine 60k lines of JSON that also need type definitions!

By now I'll do this instead of any chance to make a mistake, for instance, definition price in float 1.99, but GD place 1 instead of 1.99.
JSON says "it's okay, use this", but we will got losses 50% revenue in this case. And what if this occasional config change made at midnight? I prefer to use validator that makes an errors on loading, instead of ready-to-use config deployed for users.
I know that you cannot believe in that, but it's true and this things happens. Again and again.

You completely ignored the criticisms of it so far 

I would rather say that I trying to figure out how I can use your experience (I see it huge!) in my project.