First of all, the elephant is not the most expensive tank destroyer in the game, the ISU is by 35 fuel and some manpower.
Secondly, Soviets have no infantry-based AT so yes, of course you have to counter the Elephant with combined arms.
Thirdly, I don't have a problem with people working together to destroy artillery. The problem I have is that the Elephant doctrine comes with everything you need to counter anything the Soviets could possibly throw at you.
Fourthly, the ISU is just as OP as the Elephant if not more OP right now. Both need hotfixing ASAP.
That and all artillery is currently a bit naff.
Also that twitch video has a few extra commanders in the commander selections