I think savathuns ultimate goal is protecting the traveler from the witness. She's deceived many in her time, but the most impressive deception of hers was the witness. She knew that if her plan to take the traveler failed, then we were the next best ones to protect it. That's why I think she spent her time as osiris forging an alliance with the cabal and removing the political enemies of the vanguard to unite the city. I think she also gave crow his memories back to make him feel responsible for taking on the leadership of the hunters (which we still have to see come to fruition). Who knows, maybe she knew that he would feel the guilt of uldren and that would make him kill the psion and then Saladin would join the cabal, further cementing our fragile armistice into a unified alliance (although that seems a little too specific even for savathun). She even says as much to us when we kill her at the end of witch queen "the game is now yours to win or lose." To be clear, I DON'T think she did these things to protect humanity. I think she did these things to protect the traveler and resist the witness. Savathun is still responsible for millions of human deaths and the suffering of many more. She isn't an ally of humanity: we're just a pawn in her game with the witness that she needs to keep on the board to win.