What a US 5.4-inch gun would change

If the US Navy adopted the 5.4-inch gun, would it merely delay the 5-inch caliber?

It would likely replace rather than delay the 5-inch path, with better surface effect but worse handling and anti-aircraft compromises.

The larger shell improves anti-surface effect but moves beyond the handiness of the 5-inch/38. Square-cube scaling increases shell mass, which affects sustained loading, crew fatigue, mounting assistance, and the number of guns a destroyer can support. Larger cruisers and battleships could use powered assistance to sustain roughly fifteen to twenty rounds per minute under the assumptions discussed. A destroyer relying more heavily on manual handling might instead need two or three additional people per gun to maintain fire. Those extra crew then drive secondary demands for accommodation, food, water, medical capacity, and electrical power.