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The behavior is expected.
Widget Libraries and Typography settings are mutually exclusive. The font and size settings for the latter are only applicable if you are applying text to any of your widgets.
For widgets in your imported library, you can use Widget Styles. These are reusable, centrally managed sets of style properties. You can apply a single widget style to multiple widgets in order to unify their styling. If you change one of the property selections in the widget style, the change will be applied to all widgets using that style.
To apply a widget style to one or more widgets, select the widget(s) and then select the widget style in the widget style dropdown in the Style pane or the style toolbar.