The Thunderclap Ninth Heaven wasn't easy to cultivate.
At the time, in order for Ling Han to achieve initial success with body of lightning, he was struck by lightning for several days. To improve the body of lightning, he'd have to be struck continuously by thunderbolts to absorb the essence within the lightning, gradually improving.
This was a very slow process. From Ling Han's initial success till now, the steps he'd made were pathetically small, but it couldn't be helped. The lightning might look extremely frightening, but for a body of lightning, the essence of lightning contained within was extremely little. Being able to reach great mastery within fifty years? Ling Han already thought that it'd be extremely fast.
It indeed was fast. The great mastery of lightning body could correspond with the Shattering Void Tier, and how many Shattering Void Tier elites could achieve this level in fifty years?