Perhaps, this was exactly what the saying meant --- one good turn deserves another. Had they only went to devour some heavenly beasts to increase their Saint Energy, only God would know how long it would take them to absorb 3,000 drops of Saint Energy. After all, the number of heavenly beasts that were at least at the Heavenly King tier and above were very, very limited, even if it was in the Heavenly Snow Mountain. It was absolutely impossible for them to simply devour them and transform as they wished.
However, the amount of energy contained in the Destruction Energy was so incredibly vast. Both Zhou Weiqing and Tian'er could clearly feel the increasing speed of the huge Saint Energy Whirlpool that was at their joined hands.