Yes the issue is present in fresh instance of AEM 6.3+SP2 and AEM 6.4.  Observed in we-retail templates and pages.

Style system is not visible in component's toolbar for components which are embedded into another component (Component A) using data-sly-resource.  The parent component (Component A) is added as a default component at template level (Editable templates).For the same embedded components style system ...