Yak-9T - incredible firepower (or maybe incredible tank's lack of armor?)

[JtD]

There are explosive AP rounds.

Aircraft weapons were very well capable of destroying tanks, the biggest difficulty was to hit the target. And that was easiest with guns.

One can also be sure that a single hit of say a 100g projectile of a 20mm cannon penetrating armour and then exploding inside the tank would not always destroy the tank. That's something not even a ~6kg round of 75mm cannon would manage all the time. But, nonetheless, against medium tanks say up to Pz IV size, even the small 20mm cannons did occasionally work as tank killers, provided they had a high muzzle velocity and a heavy projectile with decent AP qualities. The Hispano for instance had all that.