He's not actually wrong, the AoE radius reduction along with the insane drop off of damage at far means that you can actually kill things (tanks and infantry) in a radius of 6. The AVRE will be able to 1 shot infantry in a radius of 6.75 after they reduce it's damage to 440, right now it will 1 shot (tanks and inf) in a radius of 6.75 and almost kill an infantry outside of that radius (to a max of 8).
So until they fix the drop off in AoE damage for the Sturmtiger, it's basically useless against anything that can move at a speed of 3 or higher (which is all infantry and tanks).
And whats wrong with it?
Avre kills infantry better(when you're dumb enough to get his by something so slow you see coming)
and st one shots mediums.