User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-41.13.60.185-20190802071906/@comment-10330822-20190802080004

Yes, but also because it diversifies the Rating Games. Rather than just devil-on-devil matches, he can fight all kinds of opponents, including gods. Which helps Issei power scale without something like an actual war happening.

High-Class Devils are leaders, they are kings, so the measure of their success is in how they lead. Also, if he is to become a Satan, then he will need to be successful as a leader, because the Satans are the leaders of the Underworld.