Why timing mattered more than redesigning British carriers

What needed to change in British aircraft-carrier design?

Not much in principle; the carriers needed to be built earlier, while making them larger depended on 1930s technology.

British aircraft-carrier design did not need a sweeping change. The ships needed to be built earlier so that useful capacity existed when war arrived. A demand for substantially larger carriers would also require adding features and technologies that only became available during the 1930s. Carrier capability in this counterfactual therefore depends as much on procurement timing and technological maturity as on drawing a bigger hull.