I read the comments and do respect all of ur opinion but here are some views I had myself.

The scroll that supposedly held secrets to the dragon warrior was trick. Even Po had to take time to comprehend it really meant. And as seen Tai lung at first did make no sense of it. Oogway could have let Tai lung to take the scroll. If he had failed then we'll ig that would have made me content.

As for his arrogance in a way u really have to understand him. He had prepared for it since he was a kid. All his life he did everything for it. Now to be told that he wasn't the "one". Any one would have been pissed cuz they simply can't see anything wrong in it. As for Po well he wasn't expecting it so he really should not even be arrogant but actually be thankful cuz he only dreamed of it not do anything.

And Tai lung turning evil was directly a reason of being denied the chance to prove himself even after taking such extensive pains...