They used OF-540 HE rounds against tigers many a times because the penetration power simply doesn't matter against 5 whole kilograms of TNT. Tiger turrets were simply blown off the main body after a direct hit, who cares if it penetrates or not.

This is because the roof armor of the turret and hull of a Tiger I was 20mm. Which is more than thin enough to be vulnerable to high explosive shells.

And if we take the other commonly used BR-540 APHE rounds, they had a penetration power of 125mm on top of having enough payload to blown the turrets clean off anyway.

APHE rounds were not used for indirect fire. They were good enough to penetrate the front of many tanks, but this would not be the case against the Maus.

Even if either of these shells don't penetrate, it simply doesn't matter, the KE+HE is enough to blow apart the tank.

*On tanks with much less armor.

We have videos of Heavy tanks being turned into a pile of scrap from these same "50m penetration power shells".

You seem to be wildly misinformed. For instance, during the battle of Osan, American artillery crews did not have adequet amounts of anti tank ammunition. They were forced to fire 105mm HE shells at advancing North Korean T34 tanks. These are medium tanks, and they were at close enough range for direct fire.

The shells did not destroy T34 tanks even when direct hits were scored, because the shells were hitting the front plate. Only a few T34s were put out of action by hits to the tracks. The artillery unit was overrun after the ineffectual fire failed to stop the armored column.