If realistic examples of anime adaptations have shown us something is that the adaptations that look the most original are the most beloved by the fans. The anime shouldn't make the original source more generic. It should make it more unique, add to what it already has and compensate for what it lost.
For example Boku no hero Academia, Naruto, Bleach, One Piece and Jojo's. The character designs and overall quality of the drawings is arguably less impressive in the anime than in the manga, BUT all these shows have amazing soundtracks, animations and voice acting.
On the other hand, HunterxHunter (2011), Haikyuu, Shingeki no Kyojin, Mob Psycho, etc. These ones are MUCH better than the manga because the art is better than the original source and they also have excellent voice acting, soundtrack and animation.
Generic means that it can be forgotten easily. And Mainstream doesn't mean generic, it means that it's popular, and we can agree that many mainstream anime look VERY different and have almost no similarities in the character designs.