He did, but it was just a fleeting moment of happiness for him Mikasa, JSC and co. And even that came at a massive cost because that's how Isayama rolls: he got a life expansion but it'll only last for thirteen years and in chapter 90 Armong lost the person he cares about the most, ie Eren, for good. They don't understand each other anymore and you could hardly say he's happy right now.
As for the Erwin stuff, I do think he's not quite being portrayed as his successor. He's clearly been struggling with the notion of sacrifice and what it actually entails but after his near death experience he's seemingly come to the conclusion that losing one's humanity is not necessary, while the reverse happened for Eren. I'm honestly curious to see where Isayama will take their relationship.