[timr]

I know what p-hacking is. There's no reason to believe that they've done that here. The choice of enzymes was motivated by the logic they outlined in the paper, the enzymes chosen are some of the most popular today, and the authors are completely forthright that the choice might affect the outcome.

To fairly make a critique like that, you need to have at least some evidence that a selection bias was applied for no other reason than to affect the p-value. Otherwise, literally every study can be accused of "p-hacking". Here, there's a very good, obvious explanation for the choice that they made, and therefore all you can really say is that the results might be different if you looked at a different set of enzymes.