I think it pulled back in terms of time. Lux's bio as it stood was pretty much "complete"
She had gone through her heroes journey without much supplementery material. She accepted her powers, met Galio, discovered the Illuminators (which are still mentioned in the new bio, Lux just doesn't know yet)
I feel like this at least gives her somewhere to go. Lux before felt like Genji from Overwatch an interestin character but one that was already 100% developed and found their place in the world. She was a less interesting Taliyah from a narrative perspective, because Taliyah has much to learn and places to go but Lux is just sorta done. Now she has somewhere else to go.
I was much more upset about Garens bio changes taking the focus off of Garens' uncle dying and his reaction (which made him believe in Demacia) and strangely Jarvan IV getting captured is completely missing.