Im not sure I guess the balance team were trying out a lot of things early on so you saw wild swings in balance whereas now they make small changes comparatively, according to the changelog the elefants damage hasnt been more than 320 and isu's health lower than 960 but it clearly took more than 500 hp in that hit.
320 hp in one shot... 2 shots of damage, and considering that if most tanks did 80 damage with the main gun... the elephant did 4 shots worth of damage... Could you imagine??