Treaty cruisers at 12,500 tons

What if treaty cruisers were limited to 12,500 rather than 10,000 tons?

Japan might still exceed the limit to gain an advantage, but Britain could use the extra displacement to produce much more capable County- or Town-type cruisers.

The extra displacement would give designers meaningful room for armour, weapons, machinery, or endurance. Britain could apply the margin to stronger County- or Town-type cruisers rather than merely enlarging the same ship. A Japanese move toward an 18,000-ton cruiser would then face more capable legal designs from rival navies. The competitive effect depends on what every signatory can do with the higher limit.