User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-2602:306:CD9A:C860:1999:D3D0:B3E7:CF47-20190219114510/@comment-34061653-20190222184108

"Rias team has become strong without Issei"

This point was made clear on multiple reasons because not only has Rias proven she can be strong without him but she even improved. Issei waa not only her strongest fighter but also the one for her collabortation technique [Crimson Extinct Dragonar]. However Rias not only replaced Issei with a stronger pawn but also created a stronger collaboration technique in the form of Gasper [Forbidden Invade Balor the Princess].

Furthermore, Rias gathered allies to her team without Issei's influence like Xenovia and Asia was. Hence why she she gave Rossweisse to Issei and wanted a fresh start with the peerage members before Issei came along. Hence she recruited Valerie, Strada and Crom. Lint was given to her.

Lastly, while it's true that Issei has Ravel to replace Rias for his tactician, the difference is Issei has rely too much on Ravel. This was pointed out by Indra due to Issei's inexperience. If Ravel geta taken out then Issei's team would collapse. Rias is a different story because she doesn't rely on Crom that much. Even if Crom was taken out, she still has Kiba who is her ace and her Balor Form which is strong enough to fight gods. In other words, Rias has other options unlike Issei.

Again, you arw missing the crutial point. Rias has experience leading them. That's the difference between her and Issei. A leader is what keep a team together and function properly which is something Issei lacks. Even though Crom, Strada, Valerie and Lint has never worked with Rias, they are still able to function well as a team due to Rias leadership. Again this was pointed out in volume 22. Rias peerage has been with her for years. Even in volume 1, we saw how well they function as a group when Rias leads them and it haa been that way throughout the story.

Again, she was taking her teammates feelings into account. Recall when Rias recruited Strada. Strada wanted test the young generation of swordsmans. Arthur, Xenovia, Irina, Cao Cao etc.. Given Xenovia is Strada's successor, it'a natural he would want to fight her. Crom wanted to fight Fafnir and given how troublesome Asia is if she was left alone, it would have to be Crom to do it. Given how hax OP Asia is, Crom was the only one strong enough to defeat Asia and Fafnir.

So that leaves Kiba as her best option left.