Just War Theory doen't apply to abortion. We should set aside false analogies like that.
There may be extenuating circumstances in specific cases...maybe even a lot of cases. But, it is improper to make a blanket exception based on a theory that has no application to abortion.
Regarding to absolution by priests: I had thought you were referring to something new by Leo. I see now that you are referring to the one year delegation of absolution for abortion to all priests during the Jubilee Year of Mercy in 2016. I have no problem with that historical move, and even if it were initiated again by Leo, I would support it. It does not imply that abortion is somehow less sinful, though, pursuant to Church Doctrine. It is merely a change in discipline, not doctrine.