They would have very useful, not Earth-shattering, but handy. The ability to conduct all flight operations, both landing and launching, in the same evolution would have been a great help, but if everyone was using it it would mainly even out.
One difficulty would have been that the standard methods of deck parking strike packages would not have worked and something close to today's system would have been needed. That would have required some serious rethinking by air bosses.
Another issue would be that every carrier pilot would have to be retrained (this was the case for the USN & RN when the angled deck came into use, but it was during peacetime when you have time for that). Landing on an angled deck is, frankly, weird as hell. You can't fly straight at the carrier you have to come in off axis and land on a moving target, at an angle. Weird. Now if the angled decks were in use for some time before the war, it would be less of an issue.
The other difficulty would be less of a problem, but still a pain. That involves the Cats. Even though, by 1943, pretty much every USN carrier used catapults to launch aircraft they were hydraulic systems, not the much more efficient steam cats that are in use today.