Why a 6.1-inch gun adoption could displace the 5-inch/62

If the Royal Navy had adopted the proposed 6.1-inch gun in 2014, would it still need the 5-inch/62?

Probably not, because a navy that had just introduced one new gun would be unlikely to adopt another only a decade later.

If the Royal Navy had introduced the proposed 6.1-inch gun in 2014, it would probably have had little reason to adopt the 5-inch/62 in 2024. The earlier procurement decision would already have provided a new gun system. Introducing another after only ten years would be difficult to justify on the reasoning given here.