Tsushima was situational though, as fireproofing and firefighting gear were primitive. Beside paint, flooring, furniture and wall panels all being more flammable than in the World Wars, damage control parties and water hoses and mains were exposed to shell splinters in ways they weren't on later ships. By the Second World War, aircraft carriers excepted, fires very rarely resulted in the total loss of a ship.
"Cumulative damage" was not something naval designers pursued, as we see with the development of all-big-gun armament after, and as a result of lessons from, the Russo-Japanese War. Better for a 12 inch shell to cause major damage than a 6 inch shell to start small fires. In addition, rate of fire was demonstrably not the same as rate of hitting, and as fire control equipment improved, and ranges increased, the emphasis became clear - hits by large calibre guns that could defeat armour.