Difficult And Redundant = Useless.

That means he can copy an attack he has seen before without needing to see it again. He needed the help of his Shard of power to do that but the result is underwhelming. Copying from memory is redundant if he has unlimited copying. He doesn't need to copy from memory as long as he has unlimited copies of the ability.

Unlimited copying and copying from memory are wonderful on their own but wasteful together. He can do one on his own while the other one needs the interference of his shard of power to do because it should be impossible. It should be impossible to copy an ability he has seen in the past since his mark of sin won't be able to activate in real-time to copy it. Now he can have a simulated activation of his mark of sin but what use is it if he can make unlimited copies? He wouldn't need to copy from the past anymore if he already has unlimited copies.