This blog post is about using these operators to bypass WAFs. You don't need JSON operators for that. You can substitute `1==1` with `2==2`, or `1!=1`, or `true`, or a million other approaches. There are an infinite number of such strings.

This is a problem with WAFs, not databases. Postgres and SQL Server both provide prepared statements as an alternative to string concatenation, which addresses SQL injection. (Though some people may be stuck with legacy or vendor-contolled systems that they can't fix, and so WAFs are their only option.)