User blog comment:B214/Volume 22 spoilers/@comment-27083298-20161112215056/@comment-10330822-20161114063140

Exactly. Hence why Crom would be a nice stand-in for Issei in the WRC. That also could explain how Rias's team is actually going to stand a chance against Issei, because they have Crom. Because if they don't have Crom, its going to be a smash fest, just like if Issei's team doesn't have Issei, but Rias's team has Crom, then it would be a smash fest on their end.

That is probably what their fight is going to look like if Rias and Issei's teams fight. Issei would fight Crom, and Rias and Akeno would probably fight Bina Lessthan, who is probably Tiamat, while the rest of the team fights amongst themselves. The winner would ultimately be whoever wins between Issei and Crom, because when one falls, the opposing team won't be able to handle the victor. Of course, Tiamat, if that is her, might be able to fight against Crom, but he is said to have Heavenly Dragon-levels of strength, equal to Dulio, who is considered to be near Seraph Angel power ranking. And that isn't even including whatever special power he has that had him called the "Crescent Circle Dragon". So Tiamat may actually not even be able to handle him either.