User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-114.142.170.11-20191120214811/@comment-87.14.182.73-20191202001754

Gabriel won't be part of it because even if there were more women, they were represented by their naked breast and Issei didn't recognize anyone of that, and Issei has an archive in his mind in which he collects perfectly the shape of each breast he has saw in his life. He saw Gabriel's breast and confirmed it as the most beautiful he ever saw, and her breast wasn't among the ones he saw in his dream. So nope. Gabriel hadn't to be important to Issei to substitute Michael, she was just the only seraph that had been already introduced and had some dialogue with the gremory group before, so of course she was chosen to replace Michael, that way Ishi didn't have to introduce another character.