When Heaven and Earth Rules dealt with internal strife among its own, the suppression it imposed was far greater than what outsiders suffered, because even every wisp of Immortal Essence the suppressed person inhaled belonged to that world!
Under such suppression, aside from the Imperial Spirit, which could transcend it and remain unaffected, it would be difficult for more than half of your abilities to be brought into play. Qin Huang, on the other hand, would see his strength surge under Heaven and Earth Protection.
Qin Huang was not truly weak. After one side rose while the other fell, fleeing in disarray would likely be your only possible outcome...
Conversely, now that you had been granted the great mantle, Qin Huang had become far less troublesome to you. You were even confident that you could kill him within Qingming Hetong Heaven. From this alone, one could see why, in many worlds, rivals who had originally been evenly matched would find the other side suppressed so thoroughly they could scarcely turn things around after one obtained the position of co-lord.
Yet unless it was necessary, when one held absolute control, there was no need to kill at all costs—like Luo Ye and Shen Ming of Seven Luminaries Mo Yi Heaven. You had previously believed Luo Ye could not kill Shen Ming, but now it seemed that might not have been the case. Luo Ye was likely considering his own interests, or rather, the interests of all Seven Luminaries Mo Yi Heaven.
After all, Shen Ming possessed the cultivation realm of a Star Sea Quasi-Emperor, and the many treasures on him had added considerable Heavenly Dao Origin to Seven Luminaries Mo Yi Heaven. If Shen Ming were casually killed by Luo Ye, Seven Luminaries Mo Yi Heaven would inevitably suffer no small