In the past, CNN would never have included the sentence speaking of the how some had hoped that he would focus his attention there - mentioning the work he did as a Senator. Think back to 2004 - though some spoke of his work on the POWs, there was absolutely nothing on the fact that he is credited with working out the compromise that the UN and Cambodia used for trials - in the long ago Prosense thread, it surfaced again when the UN used the procedures in Sierra Leone. (Then think of the inside the beltway garbage when he was not picked as SoS that it was because he was a lightweight -- I suspect by the same people who diminished Biden as soon as there was speculation that he would run in this year's race.)
I think being (other than Obama in both cases because the go ahead of the President was obviously needed) the essential American in getting both the Iran deal, that very possibly avoided what would be a worse war than Iraq AND the essential American in getting the China/US climate change pact and the Paris agreement on climate change. Others can claim they were important in either of these - and in both cases there were many many people who worked hard to get where we are), but these are both part of Kerry's legacy.
In addition, for those who do not think he has an over reaching vision on foreign policy, it is mostly that he has one that is a VERY major shift from their POV. This includes most of the "foreign policy experts" - most are neo liberals or neocons. What is interesting is that many of them are grudgingly respectful of his ability as a diplomat. This is significant because it is (limited) praise for someone working against their goals. (google Aaron David Miller or Michael O'Hanlon for two neo libs.) If they shy away from conceding he is as significant as Kissinger and Baker, it is fair to say that it is because they actually agree with a foreign policy - Kissinger's and Baker's - that most of us think wrong .. and immoral.
The Iran deal really is a done deal. It is international and there really is no Republican gain in pulling out. While they can impose US sanctions - they will be more ineffective than the unilateral Cuba sanctions. As long as Iran is not violating the agreement, there is no chance of getting the rest of the world to agree. In fact, all that happens is that US businesses are excluded from a potentially lucrative market. Climate change is more fragile - but with any luck, the agreement has tipped the balance towards green energy. One question I have - far outside my knowledge that I have not seen answered is - would the energy companies that change their power plants to comply with the EPA have any real economic incentive to change back -- or are the upgrades or changes now sunk costs? (I know one answer is elect a Democrat so we don't have to find out, but I wonder what the economics at this point are.)