As the title says, during this year we were introduced to 9 legendary skins and the distribution of them went like this

Irelia (First Legendary), Riven (Second Legendary), Karma (First Legendary), Master Yi (Second Legendary), Viego (First Legendary), Soraka (Third Legendary), Nami (First Legendary), Kayn (Second Legendary) and Senna (Second Legendary). 5 repeats and 4 new comers to having a Legenday skin.

If you consider Xayah/Rakan alternatives + Samira(Ultimate), the gap stays at a similar level, with 7 legendary skins being on champions who already had one and 5 on first time champions.

I feel like the game has enough popular champions that the distribution could focus on champions who don’t have any Legendary skins yet.