That seems like a bit of a stretch to me. We have no idea as to when the writers knew about Iris being the Champion in B2/W2 and aside from maybe getting a Dragonite
, I don't think that we can say for sure that the quality of her writing is the result of her role in the games. Even if we could, I don't think it would matter in the long run simply because anime Iris is different from video game Iris, just like Bianca, Brock, and Misty are different from their video game counterparts. It isn't necessary at all to make Iris look so strong in the anime just because she's the Champion in the new games due to how different they are. Bianca is still a primarily comedy relief rival in the series, but I'm pretty sure she's not like that in the new games. Honestly, it would make the writing around Iris feel a bit worse if that was the reason she's been glorified and everything has been resolved for her, especially when they had established her immense amount of flaws early on in the series. Considering that, unlike with Misty, the writers had plenty of experience with developing female characters and had gotten better with how they handled them in each new series, the way Iris turned out feels like a perfectly valid indication to how girls with no sidequests would be treated. At the very least, Iris' treatment does not give me any hope for another female character without a battle active sidequest would turn out any better.