This statement makes it appear as if Paxson was aware of the movement in the late 1800s of the attempt to make history a more scientific endeavor by writers like Bernheim, Langlois/Seignobos, and others, but that Pomeroy is less so.
How scientific can history be as an area of study? There is the descriptive from which we might draw conclusions, but how much can we know when there are not only so many potential variables, but we generally lack the ability to design and run discrete experiments on history itself?
Recall Paxson's earlier comment that "in history you cannot prove an inference".
https://hypothes.is/a/LIWSoFlLEe2zUtvMoEr0nQ
Had enough time elapsed up to this writing in 1953, that the ideal of a scientific history from the late 1800s had been borne out not to be accomplished?