Why Kawachi's mixed barrel lengths were exceptional

Did any other post-1890 capital ship combine one main calibre with different barrel lengths?

Few, if any, comparable ships did so because similar-looking guns with different ballistics complicate maintenance and make fire control extremely difficult.

Kawachi combined guns of the same nominal calibre with different barrel lengths. Their shells were similar, but their engagement ranges and sighting requirements differed enough to complicate targeting. Correcting the fire of near-identical weapons with different performance could become confusing. Maintaining the different gun patterns added another difficulty. These disadvantages explain why the arrangement is described as exceptionally rare.