Its not as clear cut as tabulated data on number of barrels cargo because the Lewis and Clark design has a range of 14000NM at 20kt, or more than twice the range attributed to the Cantabria. According to Global Security it is USN practice to count any fuel over what is required to achieve 10000NM as cargo with this class having 25000bbl bunkerage, plus either 18000 or 23450bbl cargo. Rough calculation assuming a required range in RAN service of 6000NM (as for Cantabria) that gives the AKE another 14280bbl for a total of 47700bbl or 7580m cubed which is much closer, drop the speed requirement from 20kt to 18 or even 15kt and the fuel available for transfer will pretty much match that of Cantabria.
All of the above is without any changes to the layout of the basic ship, with a new build there would be little difficulty in significantly increasing fuel stowage by reducing dry stowage. What is interesting with the design is that its dry cargo areas are reconfigurable between ammunition, dry cargo, refrigerated and freezer capacity in addition to fuel and potable water.
So in an apples for apples comparison to the Cantabria, i.e. 6000NM at 18kt the Lewis and Clark quite probably has a similar volume or transferable fuel but much greater dry stowage as well as the flexibility to carry general cargo, military equipment and the possibility to convert some of the space for other rolls either through the use of containerised systems or even permanently outfitting compartments.
These are big ships but very modern and efficient with their medium speed diesel generators feeding an all electric propulsion system and the latest in efficient cargo handling systems. They are very well built to worlds best practice, NASSCO being the bench mark for such civil / military construction. Yes South Korea, Vietnam and China can pump out bulk carriers and oil tankers fast and cheap but they can not compete on complex vessels like these which were designed using 3D modelling (Catia I believe) with a methodology more akin to an airliner or state of the art factory, they even modelled forklift access to shelving and time and motion studies. They are the sort of ship you could justify building locally with the proven assistance from General Dynamic (engineers and specialists from BIW also move around NASSCO and EB as required by project load, these are some of the people who were brought in at great expense but their advice was ignored on the AWD).
Three modified AKEs would easily cover the AOR and strategic sealift roles with the possibility of being easily modified to offer a level of maintenance support, less for the RANs escorts but rather small craft, vehicles and possibly helicopters.