Playing Devil's Advocate: if this is the case, why did it take until the last week of his tenure as President for him to do this?
No, this smells of "legacy". Obama could have done this years ago.
Because the petition on which action was taken was filed by Manning in November, and the review that goes into making the determination takes nonzero staff and Presidential time, and wasn't the sole thing the White House was doing.
However, if the supposed motivation is because somebody is suffering...why wait another day, another week, another month, another year?
If this took place before the election, you could call it a principled decision.
If this took place immediately after the election, you could call it a cautious-but-nevertheless-sound decision that might have otherwise been passed on to a (presumably friendly) successor.
Instead, this has taken place three days before he leaves office.
Manning hasn't gone anywhere in seven years. This was not based on a long bout of soul-searching or a sudden new development.
This was a move to either bolster Obama's legacy, or grease the wheels for a post-Presidential opportunity.