Henderson treated the York class as a design warning

How much was Reginald Henderson involved in the York-class cruiser program?

Very little; the class largely predated him, and he later used it as an example of what not to do when developing the Crown Colony cruisers.

Henderson was not deeply involved in creating the York class because most of that work predated his influence. He used York and Exeter as warnings while developing the Crown Colony class after the Towns. The Crown Colonies are described as stripped-down Town-class cruisers intended for faster wartime construction. Pauses in their production are then criticised for undermining that intended advantage.