This theory makes exactly the same observational predictions as your current best theory of physics, so it lies in the same equivalence class and you should give it the same credence.

You're blurring an important distinction between two types of equivalence:

• Empirical equivalence, where two program-theories give the same predictions on all currently known empirical observations.
• Formal equivalence, where two program-theories give identical predictions on all theoretically possible configurations, and this can be proved mathematically.

If two theories are only empirically equivalent, you use the complexity penalty and prefer the simpler one. If the theories are formally equivalent, you don't bother trying to tell them apart. If you don't know which equivalence relation holds, you sit down and start doing math.