Json schema does scale down pretty well (indeed as the link above shows the simplest possible Json schema is just "{}") - it also has pretty good tool support (e.g. VS Code) - there is a Json schema for Json schemas which helps a lot.

The main advantage of the approach in the article appears to be that its easy to extend validation with code - which is a nice touch. Pretty much any complex Json validation I have written has to combine both schema based validation and code based checks - usually done completely separately.