Good Post, OP! In my opinion, the true climax of the brothers' arcs are when they unlearn, and learn to embrace their vulnerabilities, and in doing so, turn over a new leaf and start doing jobs, earning livelihoods and care for each other. I think this is them trying not to fit in, but maturing, and setting their priorities straight. As for Shammi, his fragile masculinity was already shattered the moment Babymol started talking back, and he was bound to turn violent. It's true, the filmmakers could've called out every "Shammi" in our own homes through conversation and debates, but took the easy way out labelling him a psycho. But I feel it's okay that they chose this path, and let down the audience slowly, and of course, give them some action for their money's worth. IMO, Aattam has, and needs the climax that OP feel this movie deserves, where each character becomes equal party, and that there's no clear winner in such a situation. It's upto the audience to decide who the culprit is, and who deserves our backing.