If Ling Han ventured to the Netherworld, of course he could complete his comprehension of the Regulations. However, the Netherworld only had its own set of Regulations. This was unlike the Celestial Qi, which contained both the Regulations of the Immortal Realm and the Regulations of the Netherworld. Compared to comprehending a single set of Regulations by itself, comprehending this Celestial Qi was a complete breeze.
It could be said that comprehending Regulations in the Netherworld for 10,000 years wouldn't be as beneficial as comprehending Celestial Qi in this place for a mere two hours.