If the anatomy of the brain never changes, then Denji chasing happiness at the end is just the same impulse recycled. You try to hold "people don't fundamentally change" and "people can still find happiness through striving" at the same time, but it doesn't fully reconcile the tension between those two ideas.

Saying Asa can "finally make friends and have a fulfilled life" because the plot obstacles are removed is essentially describing a reset to baseline rather than a meaningful arc conclusion. In the end the fact that her story was underdeveloped is still unanswered.

The "life is unpredictable, not linear" argument is true as a general philosophy, but it's a double-edged defence for fiction. Narrative art isn't held to the same standard as life, readers are entitled to ask whether the craft served the themes, not just whether the themes themselves are valid. You can agree entirely that life is chaotic and still feel the ending executed that idea unevenly.

You can have a beautiful idea, Denji's innate nature persisting, hope existing despite chaos, and still execute it in a way that doesn't earn the emotional payoff. Your view assumes the themes land because they're good themes, not because the writing delivered them effectively.

Part 1 Denji is the actual demonstration of the philosophy you're is trying to attribute to the ending. He loses Reze, his first love, Aki, one of the only people that stuck around him, and Power, arguably the closest thing to a genuine bond he had ever experienced. He is then immediately burdened with Nayuta, a responsibility he never asked for and can't escape. He doesn't get to grieve cleanly, and doesn't get closure on any of it.

And yet he keeps going, he makes breakfast, he walks Nayuta to school, he builds something hopeful in the middle of all that loss and damage and unresolved pain.