I think there is a gap, but it's not what they think it is - it is the gap between description and execution. Chalmers wants a description level explanation for the properties of execution, which is not possible. He wants to get for free what is an irreducible recursion between cost and action. The gap is not ontological, it is epistemic.

It just means we can't know without paying the price, walking the path of the process, step by step. No jumping ahead. We can't even predict a 3 body system far ahead. We can't tell the properties of a code without executing it. We can't compress most processes, their execution is the shortest description. Chalmers wants 3p to eat for free at the table of 1p.