It's hard to quantify how "different of a person" you are. But if there's one thing reading psych literature taught me it's that traits like aggression and compassion (or lack thereof) are measurable and shockingly persistent in people over decades.

Circumstances, triggers, and incentives change wildly. The world is in flux. But people's attitudes generally are not.

There's a huge difference between "can't" and "don't." People can change.

I have a degree in psychology and I would love to know which studies you are referring to there because I am not aware of such well established facts.