User blog comment:B214/Shin DxD 1 discussion/@comment-39.51.215.62-20180729132638/@comment-28884330-20180802000610

"Cant even hurt Crom whith his Crimson Blaster+Dragon Slayer" This is false. Issei straight up tore his wing off, and that was with only half of the Dragon Slayer Crimson Blaster.

I agree the story gains more from Issei beating Rias, but the reason being that Issei has little wins "on his own" is kinda convoluted and strange. Pretty much no one has many wins on their own going by the ones you mentioned.