I mentioned looking in Flask-RESTful previously. It seems to be an abandoned project. A fork, Flask-RESTful is also abadoned. But a recent fork, Flask-RESTx does appear active.
A former developer of Flask-RESTful suggested some recommended alternatives in a github comment. Notably, MethodView as an alternative to Resource addresses one of the concerns I had regarding Flask.
In conclusion, I'll be sticking with Flask + libs instead of using Flask-RESTful.