Rev. Matthew Winzer:
Reformed scholastic views of the text did not operate according to modern empirical methodology. 1 John 5:7 is regularly used as if it were the Achilles heel of the TR. Whatever one thinks of the text, its wholesale acceptance demonstrates that the reformed church believed in the preservation of the Word without requiring the type of inductive, evidential methodology which is the trademark of modern textual criticism. It did not matter that it was not found in the majority of Greek mss. or how old the mss. were. Their doctrine of preservation was not dependent on the number or age of the mss.
Source: https://puritanboard.com/threads/james-white-the-received-text.92697/, Comment 9