The amount of Heaven and Earth elemental energy needed for the Heavenly God Realm was immense. Despite Mo Wuji's frightening rate of absorption of the god spiritual energy, coupled with the peak grade primal god energy here, his cultivation level wasn't increasing rapidly. Instead, it was on a stable increase while his strength was increasing exponentially.
Even so, Mo Wuji wasn't worried because he knew cultivation was a long and arduous process. He couldn't ask for much more knowing that his rate of absorbing god spiritual energy was already much faster than others. He also knew that it would be impossible to further increase his speed unless he had a grand array to speed up time.
The Mortal Dao required mighty elemental energy from the Heaven and Earth for its foundation. If it wasn't for his 108 meridians and the Mortal World formed by his World Channel, his speed might be a million folds slower.