An eighteen-inch-gun naval treaty world

How would an eighteen-inch HMS Arore and continued Tillman influence change the Washington and London treaties?

It could normalize eighteen-inch construction, replace older battle fleets before the Second World War, and produce treaty navies built around much larger fast battleships.

An eighteen-inch British ship would likely provoke Tillman to demand an American answer tied to continuing construction and shipyard employment. If treaties then preserved eighteen-inch limits and replacement building, First World War battleships could disappear before 1939, leaving much larger fast battleships and forcing Germany into an even less competitive position. The scenario also distinguishes dangerous quantitative naval races from competitions chiefly over ship quality.