What's the point of owning everyone when you can't feel the joy in it. It's like given the power to have sex with anyone you want but you can't feel the joy of your hard-on/orgasms. I wouldn't call it a mistake on his part, Harashima actually checkmated him and could of sealed him away if he didn't do the transfer. The 1st Hokage forced him to force his hand I think. There is no mistaking he's at a disadvantage not being immortal against the whole Narutoverse.