Yeah a CVN is bigger and better but we get two conventional carriers for the price of one "Gerald Ford"
Given that there has been NO carrier -to-carrier battles in the last 69 years you can argue (and people even in the USA do) that a CVN is a very expensive, and very man-power heavy, way of putting lots of eggs in a small number of baskets
If the CVA's are properly equipped they can carry enough strike aircraft and helicopters for what we need
As we aren't planning to going head-to head with the PLA (N) the new UK carriers are a good (but expensive) fit for our purposes