User blog comment:B214/Shin DxD 1 discussion/@comment-2607:FB90:3851:A5D3:0:14:ECCB:7501-20181029115052/@comment-2602:306:CD9A:C860:8D0A:FDDD:FDB6:72C5-20181029211948

That doesn't particularly explain what has already established. If this was a life or death situation then I can see your point but this is just a rating game. Meaning it's just for sport. Both Issei and Rias have resolved to fight each other in Volume 22 if they went against each other. Kiba in particular wants to fight Issei and Issei has no problem with that since they are rivals anyway. So I see no reason why he would hesitate.

When it came to Vidar, it was different situation because Rossweiss future was at stake but here there is nothing big important at stake. Rias has a strong team, but as we already pointed out, it's not stronger than Issei's team. It was different when it came to Vidar because his team was much stronger than Issei's team to which Issei needed a miracle to win. As far as a strategist goes, he has Ravel.

PS. I am well aware of Issei and Rias relationship. Issei always says he wants to he an equal to Issei for most of the volumes for several reasons.

1.) He was weaker than her.

2.) He was just a lowly servant.

3.) She's a high class devil while he was a low class.

Of course Issei would feel unworthy of her but what has changed now from back then?

1.) He's the most famous young devil in the Underworld and is known throughout all the mythologies.

2.) He's a high class devil which is the same rank as Rias.

3.) He's now independent and has his own peerage.

What more does he have to prove? Rias had to recruit the strongest Evil Dragon as a replacement for Issei since not even a god would take her invitation.