User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-2602:306:CD9A:C860:1999:D3D0:B3E7:CF47-20190219114510/@comment-34061653-20190222101658

Deathcount333, there is a difference between an experience player and an experience team. Rias built her team with her peerage members being at the center of it. While they haven't been in rating games, they have fought stray devils as team. Akeno, Kiba, Gasper and Koneko have been with Rias for years. For Issei, he's new at taking a leadership role and have no experience at being a king. Sure, he has people who have combat experience but they don't know how to function as a team. That was made clear in volume 22 when critics pointed out how sloppy his team was but Rias team had priase and won more gracefully. Rias team was more exerienced.

In fact here's a quote from volume 25

[Rias Gremory’s team was strong with the Sekiryuutei, but they were also strong without him—. That girl drastically changed her own evaluation in the tournament. She was highly evaluated on the [Scout] field as she was able to take in Vasco Strada, who was said to have reached the utmost limits of humanity that no-one else had been able to reach, along with the ultimate Evil Dragon Crom Cruach, and two other Longinus users in her team, combining all their abilities together. Of course, her servants who followed her since the early days had also grown, making it one of the veteran teams.]

I won't deny Rias made mistakes but Ravel's plan was to have Issei fight Rias. She didn't expect Kiba. With Crom and Strada occupied Kiba was the next best person as he was a countermeasure to Issei and also she wanted to take Kiba's feelings into account. Remember that Ravel learned the lesson of sometimes you have to let your team member express their feelings which is why she let Crom fight Asia and Ddraig because Crom wanted to fight them.

Having Kiba deal with Issei while taking out his queen was a smart move and she used physchological means to defeat Grayfia quickly so she can save her stamina to fight Issei. Lastly she came up with countermeasures for Issei. If my guess is correct, Rias plan was keep Issei occupied until help arrived. With dressbreak and Pailigual virtually useless, Issei would be locked in a stalemate battle against Rias until Crom or Strada arrive. Ddraig had a time limit and Strada had the upperhand against his opponents as they were getting tired.