But you are wrong. Defending driver needs to be ahead at apex and then he is able to force the other driver off. It is quite likely Max would not have got a penalty.
In fact I am 100% certain he would not get a penalty if he was ahead at apex, forced Norris off but remained on track himself. This is what is the problem in my opinion. This should not be legal. If someone is alongside you it should not be that you can legally forced them off because you are defender ahead at apex. It almost outlaws overtakes on the outside.
In this specific situation there is a chance VER would get a penalty because he didn't manage to stay on track himself so stewards can claim he was not in control of his car. Still, I don't think they would have given him a penalty as it is easier to stay silent. They would justify that both went off thus no one was forced.
What is the downside if the defender is required to leave a space when someone is alongside? I don't see any, we could get more overtakes (this is a positive as they made DRS specifically to help with it, also new aero regulations with ground effect were introduced to improve racing and amount of overtakes), we could get more side by side action in the corners (again a benefit). Only downside that could be theoretically considered is that it may make defending much harder. Not sure I agree with that, if defending becomes hard then you can easily just remove DRS and we have clean racing with hard overtakes in the corners.