I take it you wouldn't be interested in the rational behind believing this instance of gene duplication? You would rather just hand wave it and all other inferential methodology away so it doesn't bother you.
This means of course that we should not believe that large meteors occasionally hit the earth, that super volcanoes have in the past caused massive destruction, that geologic strata have a chronological order, that layers of rock crack and are refilled, that intrusions, uplift, and fold occur, and that paternity can be determined through DNA comparisons. Hell, we might as well dump all of quantum physics.
DNA can be read like a book. We don't understand all of it yet but have learned much in the last 50 years. Part of what we have learned is how to recognize events that have modified the genome in unexpected ways. The reason I mentioned the number of geological features and processes in the paragraph above is because there are parallels in the way the physical data are analyzed in the two systems.
I suggest you investigate the methods used to determine events within the genome before you brush it aside.
It's imaginary man. Sure there's rationale. But it's based on the 'a priori' assumption that evolution happened.
The hand-waving is being done by the proponents of the unobserved gene duplication event.
I suggest you investigate the methods used to infer a non-existent history before you credulously accept a naturalistic explanation that is only true because it is required by definition.
You understand that?