No doubt a deer slug will destroy an engine block, but an engine block is a brittle metallic object where a human body covered with a inch of soft Kevlar body armor is a pliable object.
Engine blocks break rather than bend when absorbing mechanical energy. Human bodies covered with Kevlar deform before breaking when absorbing mechanical energy.
You’re right. Totally different material.
I sure wouldn’t want to get hit by one, not even with a trauma plate.