What do you mean there's no evidence? That's like saying well, here's the corpse, the gun, the photo of the shooter shooting the victim....but there's no evidence of a murder.
The games and what they had Austin doing (and not doing) is the evidence.
Watch what teams with guys like Austin do. Watch what the Pats do with Edleman and Amendola for instance. These guys are always on the move, running across the faces of LBs and Safeties....not going 5 yards to a spot and squatting in front a LB. Not being run into the boundary. The entire game with Austin is scheme to get him operating in space. Simply didn't happen very often.And the relatively few times it was tried, like bubble screens, the D obviously knew what was coming.
There's plenty of evidence. But does even his potential make him worth the money they gave him? No.