Lux's high mana costs should not be an intended weakness; they're just obnoxious

High mana costs should only be a gate to extremely powerful abilities, and Lux's Lucent Singularity is hardly an "extremely powerful ability" like, say, Viktor's Augmented Death Ray (which easily does more than 50% more damage than Lux's E, AND costs less). You put a mana cost gate on Swain because his ultimate is ridiculous otherwise. You put a mana gate on Alistar because his crowd controls are nasty. Xerath's costs are super high because of his passive, which lets him get free mana for taking risks.

But on Lux? All those mana costs do is serve to frustrate you, prevent you from rushing a Luden's early, and keep Lux from being able to stand up to meta mid-laners like Leblanc, Zed, Kat, etc., who will keep harassing her for days after she runs out of mana. And even after she gets her Chalice, that 130 mana cost still haunts her and stops her from making plays when she keeps having to spam her E to stop the enemy from pushing her down.

Please, Riot, just modernize her costs. Otherwise, you are OBLIGATED to tell us why Lux's mana efficiency must be so bad. Stop letting the community answer for you, you cowards!