Why the Lion class would not simply mount larger guns

If the Lion class was unrestricted by treaty, why not use twelve 16.5-inch guns or 18-inch guns?

Because speed of construction, available gun programmes, commonality with earlier ships, and imperial dock infrastructure still imposed strong practical limits.

Treaty limits were not the only constraints on the Lions: Britain wanted ships in service quickly and needed them to use existing docks and support infrastructure around the empire. A 16-inch programme already existed, whereas 16.5-inch and 18-inch alternatives would introduce a new development and integration burden. Earlier political choices about imperial dockyard investment also limited the dimensions that could be supported worldwide. Iterating from the King George V class could therefore produce a practical nine-gun, 16-inch Lion at roughly 28 to 30 knots without starting every system from scratch.