The problem with giving the ISU-152 a switch between HE and AP rounds would make no sense.
The HE shell alone was enough to rip turrets off of panthers and tigers. AP for the ISU-152 wasn't widely used.
From a realism point of view maybe it doesn't make sense, however; from a game play perspective it makes a great deal of sense. Game play > realism.
-Tanks don't take 5-6 penetrating shots, they take one.
-The ranges on all most armor in the game would be larger than any of the maps.
-All armor would shoot thru "shot blockers".
-Don't get me started on the lethality of small arms and support weapons...
Think about blending the worst parts of the old Elefant, the JT, and the ISU-152. Armor could sit at the back of your base, likely sight for itself, one shot stuff across the map, and you'd have no clue where the shot came from. Sound like fun??