You misunderstand the reasoning behind the "rejection" of empiricism by Mises and those that followed him.
Austrian theory as formulated by Mises is based on a priori truths about human nature and cannot be falsifiable by evidence. This may sound outlandish when you first hear it especially when one comes from an engineering or natural science background, but there is a very well developed epistemological reasoning for this position that is often overlooked by critics.
The economy is composed of humans who act towards their own personal goals, whether that is to provide for their family, or become a billionare tech founder. This is a highly complex system with an incredible amount of variables (in the case of individual humans, the ordinal scale of preferences is quite literally infinite!). As such, there are no constants that can be inferred with the same level of reliability that we may have in physics like the rate of gravity on planet Earth.
Thus, empirical economic models have a much, much greater margin of error than what we have in the natural sciences, and it is therefore untenable to formulate economic theory based on inherently unreliable foundations.
Instead, as the economy is composed of humans acting and not objects acting, the Austrians look inwards and through a Kantian-esque process of introspection formulate the a priori action axiom ("Human action is purposeful behaviour.") and build their theory using logic based on that axiom - thereby creating a system of knowledge that is unfalsifiable through evidence and is always true.