Madara performed Izanagi inside of time (evidenced by the point kishi zoomed in on his eye) but delayed the activation to occur outside of time.
Itachi transferred his techniques and chakra into sasuke inside of time. Sasuke's eye learned and used Amaterasu outside of time.
VS.
Obito comes back from the dead (outside of time), drags kakashi into the land of the dead (outside of time), then transfers his chakra into kakashi (outside of time).
If you didn't pick it up yet, Itachi transferred his eye technique while very much alive and only taught sasuke's eye the ability once his chakra was already in him. Madara also activated his ability while still very much alive but only made his eye activate it far down the line. Whereas, Obito did it while being dead to the point of being a pile of ash.
BTW, your explanation for why it'd be temporary isn't going to work. The amaterasu itachi gave sasuke was permanent. From that period on, sasuke began to use amaterasu from his left eye(the same one itachi planted it in) while itachi's ama came from his right. The only thing is It took until sasuke awoke the mangekyo on his own for him to tap into that power again. Kakashi doesn't have that problem since he already has the eyes. All obito said was the power may be temporary. That doesn't mean it is, that's just a way for kishi to try to add mystery even though near no one cares whether or not kakashi keeps his BS powerup forever.
