The reason why Roy managed to overcome the only defect of the soul shard of absolute was that he hadn't merged with it like the Armored Knight.
He had consumed it, made its power his own!
However, the acquisition of this skill in such a way had come at a steep cost - it had taken up three of his precious skill slots.
[You have gained the Magical & Physical Defense!]
In addition to the Absolute Defense, Roy had also gained a high amount of passive Magical & Physical Defense from consuming the soul shard. It was a passive ability that negated 30% of all physical and magical damage he would face.
He could feel that this ability had taken up the remaining skill slots that were available to him, meaning that he could no longer learn any new skills unless he strengthened his soul.
His feeling wasn't wrong.