You make an argument for empiricism, which is only one way of evaluating the truth of arguments. For example, mathematics traditionally doesn't involve empirical study: It begins with a pragmatic premise instead, like "assume the following..." and then proceeds to expand on that assumption or find its inherent contradictions.

One of the "crises of mathematics" is that computerized proofs by exhaustion, by applying brute force to find all possibilities, make the field more empirical in nature and hence subject to experimental error.

When pragmatic arguments are used to create a premise like "this design will work best for the software", the question that needs asking is whether all stakeholders can buy into the most core assumptions, and whether all assumptions retain conceptual coherence when taken together. If the UX designer, the developer, the product manager, and the end user agree on a pragmatic theory, and all theories in play align without issue, there isn't an problem as to whether it's "really" true - and with software, the concepts and data are thoroughly enmeshed in pragmatic thinking from the very beginning: numbers are modelled to limited ranges or precisions, strings are encoded according to arbitrary mappings, and so forth.