Rigel got rid of every Player that he found on his way to another city no matter who they were. The fewer of them that joined the 3 major guilds, the higher the chance of survival for Hugo and the others. He didn't want to let the Non-Players from Earth die at the hands of Players because he managed to change the fate of Earth.
He didn't feel frustrated anymore because of the fight with Grandwell. He felt fulfilled and satisfied because he knew where he should put the bar on his growth which was still way higher than he expected. He felt motivated to grow stronger because his current goal was to meet Grandwell again so he could see the Devil at his full strength.