I would say the biggest difference between the two is Molten gives you more out of the box: input validation, doc/schema generation, ORM support, support for multipart/form-data requests (Falcon doesn't actually handle these out of the box!), etc.
Like flask versus Django.
Straight question, wouldn’t it have been easier to fork falcon and add the batteries?
* Falcon revolves around the concept of Resources, i.e. classes as the primary handlers of requests; molten revolves around functions,
* Falcon supports Python 2.x,
* automatic dependency injection via type annotations is core to molten.
Here:
Molten supports Python 3.6+. Falcon supports Python 2.6+.
Molten uses MyPy for validation. As far as I can see, Falcon does not.