I get it from a storytelling standpoint that it is satisfying to see the villains get the comeuppance, but in this story, these aren't the archetypical villains. They're just selfish people, and in that, Ayaka did get her comeuppance. Lost custody of her daughter, lost the person she once loved, lost the person she does love, lost her high-brow lifestyle, and is moving back in with her mother. Could there have been more? Sure. But we got what we got, and it's a pretty good outcome all things considered. Most importantly, it's a good outcome for Kokone.
Now for the half-brother. There should've been something more done to him. At least I can get some sort of defense for Ayaka in that she does apologize to Wataru, albeit at the very end of her projecting onto him (which is his fault for providing her an out). I feel like if we had just one more chapter to flesh things out, at the end of her rant I could see it circling back to her realizing how much of a fuck up she is. The set up is there, just no time to flesh it out. The half-brother though? Nope. He has no reason, there is no defense. He actually gets away scot-free, which is an actual "shame on you author" moment. There's no reason to forgive him, nor should he ever be forgiven, but the author wanted to show Wataru as a forgiving man. Hell, Case 2 should be Wataru going "alright your turn" and suing the brother for damages or something.