User blog comment:B214/Shin DxD 1 discussion/@comment-2607:FB90:3851:A5D3:0:14:ECCB:7501-20181029115052/@comment-108.7.145.117-20181029230905

"Issei didn't want to hand her over."

There are different walls m8. Vidar was a physical one, representing Rossweisse's future and thus had to be defeated in combat. Typhon, was also Issei's indirect target as the King of the opponent's team, however Issei couldn't be in two places at once (at least until Ddraig was released), and thus he had Rogun, Bova and Elmenhilde fight him to stall for time.

Rias is a completely different wall. She is powerful but incomparable to Issei's pure strength, but what handicaps him is her and her servants relationship to him. It is a fight between his friends and wive(s) and he is facing the problem of fighting Rias and fearing to hurt her and struggling with his conflicting desire to win and his other desire to see Rias win.

"Issei vs Dulio was just a friendly match"

That's my point, Issei and Dulio only fought because of the competitiveness and it was not a serious brawl so much as a series of clashes over the ball. This is a sort of 'warriors friendly rivalry". Rias is not a warrior nor a rival, she is a princess who loves and is loved by Issei and thus it would be counter-intuitive for them to battle seriously. Rias may be able to do it because of her being a pragmatist, but Issei, a man of emotion and passion, will have to overcome this and think strategically and fight his friends and even lovers and crush them, or lose. That is hinted at by Sakra when he points ut that Ravel is usually the main strategist in the prior games, which she does ruthlessly through her characteristic of domination, which Issei lacks.

"Issei wants to prove he is an equal"

Not in fighting ability or in his love or anything like that, but in his ability to be pragmatic, to make the hard decision; Win and risk hurting Rias (physically and psychologically) or lose and show weak resolve and hesitation.

Rias hints this herself when she recruits Vasco Strada, stating that 'if Issei must overcome THIS' hinting the challenge of fighting not for but against the ones he cares about.