User blog comment:B214/Volume 23 discussion blog/@comment-1884090-20170408001538/@comment-31137559-20170409163236

Issei isn't dumb or has mental problems. It seemed that way because Issei was a newly reincarnated devil and only had lecherous thoughts in his head. But he's a good learner. Well as far as being a tactician/strategist, he's kind of lacking. That's why he has Ravel. Issei can't cover everything by himself. That's why he needs capable servants to pick up where he can't. Issei has only been a devil for a year and just became a king. He needs to fill in the blanks on his own. After his match against Barakiel, there were no complaints about his other matches before his match against Dulio. Issei just needs to work his way into it.

And Rias wasn't exactly perfect when it came to being a king. Although her ability to gather powerful servants was top-notch among the Rookies Four, she lacked behind the others in terms of being a king. We saw it during the match against Sona. And especially in the match against Sairaorg where for the 2md-5th matches her team's weaknesses were exposed. And they underestimated their opponents because of their sheer power thinking that it would be enough. Rias never got to show off her quality as a king as much as the others did.