Concealment expert skill on carrier is a play-style choice, not a must-have. And you don't want it on certain carriers such as Ryujo and Shokaku, you want your detection range to be larger than 10km(Ryujo is already stealthier than that). You want to be alerted as soon as possible when a DD is sneaking up on you(and they'll know you are there regardless of concealment because your planes will give away you position if they are ~10km).