Right now, in my opinion, cloaking is very useful on fleets... But it is somewhat artificially held back by it being impossible to bring armies with a fleet in cloak. If we could cloak armies too, the doomstack meta would die a well deserved death because it would be possible to entirely lose a war without being able to stop them if you have all your fleets in one area, but right now the inability to actually invade planets means if you don't have a genocidal/kidnapping bombardment stance there's not much you can actually DO once you've outmaneuvered your enemy because the transports can be easily blocked off and then other than disabling shipyards there's not much you can do.