You're putting _isOptional in the wrong place, it shouldn't be a 'child' property of _pageLevelProgress, it should be a 'sibling' property.

You also don't need to include _pageLevelProgress at all in those instances. If that property it not present, the default setting is that the component will not be displayed in PLP.

If you look at the components.json that you get when you create an Adapt v2 course you'll see several examples e.g. c-95