The argument is that a proven production line matters as much as the bare idea of a larger gun. An Argencourt already carrying 18-inch weapons would make similarly armed Admirals and follow-on battleships easier to justify. Japan and the United States would then face pressure to prevent Britain from holding the only ships with that calibre. Their own Kii, Amagi, and treaty-era programmes could change in response. An 18-inch ceiling might consequently displace the familiar 16-inch treaty limit or make agreement harder to reach.
Notable Point · 1:10:36-1:18:37
Why an 18-inch ship could escalate the capital-ship race
A British 18-inch Argencourt could make later 18-inch Admirals and a higher treaty gun limit more plausible.