I don't think that they were even remotely similar, and for two reasons.
First, the Devs once said that the AE was much more advanced and user friendly than even their own mission building tools.
Second, the engine CoX was built in was designed as an in-house engine, and all of its tools and development tasks were put together primarily with CoX in mind, where as UE4 and for that matter UE3/UDK were more designed to be used by other studios for third party development of a wide variety of different types of games, so a lot of the functions were designed to be much more customizable and flexible than CoX's engine and tools were.