That’s the point for Poe, that he can now see when a suicide mission is a suicide mission instead of just an opportunity for heroism. The point for Finn is he doesn’t care if it’s a suicide mission or not, as long as he saves the Resistance. The point for Finn isn’t affected by Rose saving him either, because the intention is what matters here.
But my interpretation of the scene is that, had Rose not saved Finn, he would’ve killed himself and succeeded in destroying the weapon and therefore saving everyone/buying them more than enough time. If this was the case, then Rose was very selfish by saving him.
The situation in the end works for every character except for Rose.