Hispano MkII AP could penetrate 24mm of face hardened plate at 400 yards @ 20 degree's, the Panther as an example has deck armor that is 16mm, the MkIII and Mk IV could go through 30mm at 600 yards @ 30 degree's. The standard Hispano SAPI round has the same 20mm of penetration as the .50 M2 AP but with 10 times the incendiary content.
Unfortunately, the number of cases of Hispano-armed aircraft laying waste to the panzer units due to the cannon fire are slim to none. Even the Hurricane IIc would've been killing the lesser panzers in N. Africa, negating the need for the IID version with 2pdr cannon.
Perhaps the theoretical ability was not proven in everyday use?