More importantly, teammates' abilities were open to Luke, which meant that he could refresh them at any time.
In this regard, acquiring teammates was a lot better than the three ways for obtaining abilities, i.e. defeating, killing, or obtaining a person's gratitude.
That was because the abilities gained through these three methods were limited the moment Luke obtained them.
Naturally, the people who were killed couldn't improve their abilities. The people who were grateful to him were scattered everywhere, and it was hard to stay in frequent contact with them. Also, their abilities might not improve as quickly as Luke himself practicing them.
Defeating someone was more troublesome than obtaining gratitude. Luke had to defeat them again before he could refresh their abilities.
That was impossible to use often on a genius like Tony, whose abilities were improving day by day.
