A refitted Essex could handle modern jet aircraft...the only reason they weren't modified to do so (would have needed upgraded catapults, arresting gear, and blast deflectors) is that the US Navy had newer, larger carriers...and the fact that all of the Essex-class carriers were, by the time the large carrier aircraft came into service, more than thirty years old! Midway and Coral Sea (also a WW2 design) could and did operate F/A-18 Hornets. They were front-line ships into the late 1980's...Midway was even deployed for Desert Storm. (The third Midway, the USS Franklin Roosevelt, was never fully modernized...a combination of that, a low hangar height, and troublesome engines meant Roosevelt was retired in 1977.)