For hiruzen you are right, but for agk not necessarily.

Why?

Because edo itachi actually works quite good as a support for agk too.

Moreover, remember that agk almost always goes together with kisame samehada, so, owning 30 chakra to clear dream state is not that hard for those lineups. And about the damage reduction... The wise player just waits for kisame or for wind main standard attack to trigger a combo before using konan mystery against itachi edo tensei (the 10 chase of wind main and the 20 of kisame are full nin. Eventually also the sharks standard attack is full nin. After they went out konan mystery is perfectly able to deliver the full damage on the enemy lineup).