Additive manufacturing (3d printing) can produce some shapes which are not possible using injection molding

Agree. I was just thinking about this last night. The model I'm currently making would have to be multiple sub-components without 3D printing. Having everything as one piece, but still with a lot of air gaps, makes the finished product stronger.

Injection molding currently has access to a wider variety of materials due to its maturity (pelletized raw material)

There are pellet extruders, but generally agree that there's a wider material selection available for injection molding.