The problem is that the Vulcans, Klingons and the general public already knew what was happening. They knew that the Romulans were being cut loose. No one needed him to tell them this. If they wanted a redemption story, make him responsible for what happened. They easily could have done that. Instead, every thing that goes wrong is every ones elses fault but his. Trying to make a redemptive story around him being responsible for what others did and did not do falls flat. If it was in the power of the Vulcans or Klingons to do this, and they decided not to, that is their choice, not his. He is not to blame for that. Make him responsible. They could have, but did not. Quite the opposite.
But he is, Picard's sin here is not one of Action, but rather of Inaction. He. Gave. Up.
He didn't continue to fight for the Romulans. He abandoned Raffi. He's not redeeming himself for what he did, but rather what he failed to do, by choice.