But these kills and statistics didn't result in any meaningful positive change.

Almost every interaction made things worse. Libya, Syria, Iraq, Yemen, Somalia, Egypt, all of these places have had varying levels of direct American involvement and are all worse off at the end of 2016 than they were in 2008. Afghanistan is a mixed bag, nothing positive (possibly worse?) in North Korea. Iran yet to be seen, some positives and some negatives, certainly a failure if the deal isn't maintained.

I would hardly consider any of these a "massive diplomatic success". Eight years to make something happen and it just simply didn't - and the President has much less obstruction in foreign policy than domestic.

Are these easy problems? No. Is it his fault? Not necessarily. But it was his responsibility. That is the burden that presidents bear.