The Crown Colony class as a wartime Town design

Does it make sense to design a full cruiser and a simplified war-build version around the same hull?

Yes; the Crown Colony class was essentially the Royal Navy's stripped-down wartime version of the Town-class concept.

The proposed production method begins with a full peacetime cruiser and plans a simplified wartime version on the same basic hull. The Crown Colony class is the historical British example. Treaty explanations remain relevant, but the ships can also be understood as stripped-down Town-class designs suited to emergency construction. Their architecture joined treaty constraints with wartime economy and production speed.