Honestly, not having the kid along for the journey after that gameplay trailer wouldn't have made sense. Kratos is learning how to balance his anger and control his emotions, and he is ready to put his anger and pride on standby to be the father he wasn't allowed to be while being a slave to the Gods.
It's obvious the kid will primarily play a support role while Kratos is still the primary focus in combat. Getting more involved in combat will be his growth, from not being able to kill a stag on his own or strike the killing blow against a troll, to being able to make decisions that matter and turn into the well reasoned warrior Kratos wants him to be.
As for the axe, something had to be done. Freeing himself from the Gods means he freed himself from his chains. His chains were the Blades of Chaos, Athena, and Exile. Without those, the fixed camera angles and erratic, crazy chained blade combos wouldn't be possible. They had been experimenting with other weapons for Kratos to wield throughout the games, and it seems like they found a fit that required a new camera to really fully utilize it.
What matters is that the game is still a brutal action gore fest. If it can pull that off and fulfill developer ambitions, it will do just fine.
