>>42410398its clearly supposed to be a super powered boss battle god form thing like most rpgs have. the fact that its unobtainable is very intentional and you never fight it as a normal pokemon battle, only as a raid boss battle with a set non traditional health bar and scripted events happening throughout the battle. its a boss. not really a pokemon.
just because they label it an eternatus form in data doesn't make it any more of a real pokemon than robo tyranitar or nihilego/lusamine mecha
think about it, they dont it to be usable for a reason, cause its not supposed to be the same as the other pokemon you obtain and fight with and raise and make curry with and shit