You are right, the sturmtiger is still better because it has 1000 penetration and can fire through shotblockers. Now allies have a way to one click wipe multiple squads and team weapons. Seems pretty balanced to me. Just waiting for a USF CAS now.
Also, if you are letting the Petard hit your tanks that is a L2P issue.
from the stats it feels like they are even some how it feels AVRE is doing way more damage than 640... my ST around 85% health fire at AVRE 70% avre it still have around 30% hp left, and AVRE return fire at my ST which should have a least 1000 hp left, but it got 1 shoted. also it 1 shot panthers in stormless video which panther had around at least 700hp by the time and it got destroyed. so i felt it doing more damage than the stat on paper