lux is on the strong side, but she isn't unbalanced.
there are barely ANY viable mage mid laners.
lux is one of them and people arnt really used to seeing a strong mage with the current meta
lux has very high cooldowns (save for her ultimate) and VERY high mana costs. and she has no mobilty and is very squishy.
im not goign to deny she can land her E pretty freakly easily, but that is also her only real way of waveclearing so if she is constantly using it on your she will have a really hard time CSing. also. when he DOES alnd a skill on you her goal will be to proc her passive. at this time she has to get much closer and this is when you can usually trade her. keep and eye on her mana and check how much CDR she has and what her cooldowns are.
lux IS hard to lane against. but with the high cost of her E and the choice between using it on waveclear or you she will run out of mana very fast.
im not saying lux isnt very strong at the moment... but she isnt on the OP list.
not like
are