I suggest a change in instructors.
It is not big and cool to do steep turns without warning or briefing a student.
Every action on an instruction flight should have a benefit to the student and a "I have control" then throw the machine into a steep turn has no instruction benefit at all. In fact it is gash.
In a ppl I used to be hands on the controls for less than 30 mins in the whole of the ppl course. If there is no safety reason to be hands on the student should be flying. Even if you want to reposition the aircraft onto a heading there is still benefit in the student doing it. Apart from the fact that doing it by a steep turn knocks the student out of the learning groove you are also stealing thier flying time.
Also it gives the student the idea that it is pefectly acceptable to throw an aggressive turn without checking thier 6. Which 99% of the time you will get away with until one day you swing it right into the path of another aircraft.