Not entirely true. Your HMG will do shit in front of the ZIS guns in my previous example. You can use infantry neither to kill the ZIS guns bercause the ISU behind will erase it. So if you know what you are doing you will slowly push the Elefant with its entire suite to the edge of the map.
An Elefant can deny all armor but an ISU can deny everything. You still can cap in front of an Elefant, you cannot cap in front of an ISU without loosing all infantry that is trying to do that. Capping will win you the game eventualy, not killing the opponent's tanks. Can you put aside your fanboyism a little and see the difference? The other reasons were stated by many before so I won't count them again.
That is the reason for which I am sure ISU is OP but it's quite debatable if Elefant is.
Dude I'm bored of this fanboy shit so let's stop it both okay?
In my opinion both units should be removed from the game. Why? Because their design is balanced in a bad way. Look at the commanders, they can easily counter their counter, the howitzers. WTF is this shit? I'm reall worried because Relic said they won't rework the commanders. However this is really necessary!
Next problem is the worth of veteran units. They get killed so easily that they lose their worth during the game because imba units come to the field. I think going back to old veterancy system would be good! Balanced of course, so that the amount of veterancy is related to the size of the squad.