If this guy was really Greed, he would be a conniving businessman who steal money, manipulate the Witch Cult into his favour, scam the other Sin Archbishops into benefitting him, enjoy both food and sex, accumulate power throughout time and use every possible means to secure his survival, but Tappei is such an uninspired writter that we couldn't have that, his idea of greed is just a man who want to marry too many women and nothing else, a waste of opportunity to portray the Sin Archbishop of Greed as the most devious member of the Witch Cult.
Regulus could've been a villain who persuade his enemies into sympathizing with him, but of course he just had to be another predictable Sin Archbishop who seethe when anything doesn't go his way.