Riot usually doesn't use fan art or concepts as isnpiration, so I kinda doubt that.
I think that the star guardian team is simply based around the popular five man band setup and they just picked characters that fit those roles visually and characteristically: Lux as the leader and heart of the group, Jinx as the rival to the leader and violent team member, Lulu as the funny and childish comic relief, poppy as the dutiful lone wolf and Janna as the calm advisor and mentor.
I have made a short summary, if you want to read more into it.
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Madoka Magica disproves the "no blades on magical girls" theory
Taking an anime that is a deconstruction of the genre (magical pet is the main villain, the girls are doomed to die and transform into monsters, they suffer a lot of emotional trauma etc.) isn't really helping your point. Swords and physical combat in general are avoided in classical Magical Girls shows.
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We already have lux who should be a mid. She we need 4 other champs for the 4 other roles.
Skin lines don't need to work as a team comp anymore that was changed some time ago to allow more freedom in chosing the champions.
They don't look like magical girls at all.
They are supposed to look like young girls which often are part of a magical girl team.
I think you should have gone with Irelia instead of Poppy for top and with Diana instead of lulu for jungle.
Irelia and Diana both have weapons, fighting styles and personalities that don't fit the usual magical girls team that well.
While the current setup makes much more sense.
That said Riot probably will continue this skin line if it's a success.