User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-34061653-20190122110131/@comment-10330822-20190127012627

And what exact development are you talking about? Her relationship with Issei and his other fiancees? To me Rias should be more than just Issei's love interest. Sure, she is in the show a lot, but what exactly has she done and grown into?

The problem is Rias starts the story so much stronger and in a much higher stature than Issei. So in order for Issei to catch up to her, Rias remains almost stagnant. She doesn't really get stronger, so only gets a few new techniques, and they are not even by her design. The Extinguished Star only achieved because she drains Issei's Dragon Aura, and the Crimson Extinction Dragonar is only achieved through Issei.

That's why I feel we so much rapid development from her during this tournament, because Issei isn't there. She is pushed quickly to upper ultimate-class and gains a massive buff in the form of Aeon Balor's Balor Princess. But at the end of the day, she was still behind Issei, who beat her despite her "preparations".