This is a design preference within the campaign rather than a universal historical optimum. The appeal of 16.5-inch guns lies in their balance between rate of fire and the damage delivered by very heavy weapons. The remark helps explain the armament selected for Australia and the other fast capital ships in this scenario. Opening here gives a compact example of heavy-gun selection as a compromise rather than a simple largest-calibre-wins calculation.
Notable Point · 30:14-30:25
Why 16.5-inch guns appeal as a heavy-gun compromise
A brief campaign-design aside explains the appeal of 16.5-inch guns as a balance between firing rate and the damage delivered by very heavy weapons.