Idk what these ppl are talking about. Lux is awesome, if you play her right. Lux has to have enough tankiness surrounding her b/c if you build her as a glass cannon, you will absolutely destroy teams. They will literally have to build so much MR that your adc will dominate. If that happens, Lux has so much utility that she can then become assist god. With that being said, I don't think there is a better ult at securing kills. Ppl don't play her because they don't know how. Other mids can go past the river, get ganked and make it out. You have to become a master at freezing the minion wave. Also, you have to master skill shots, which just takes practice. HOWEVER, just like every other champ in the game she can be countered. Lux's best friend is distance so champs with gap closers counter her. Also with her build, you have to find the right balance between straight AP damage output and utility i.e. CC items and CDR. A good Lux controls the terms on which you trade damage with your enemies. Remember she is technically a support so if your team is garbage, she can only do so much. Just remember no matter what they change the names of her skills to, she got the FUNK. Its a mighty weapon which can destroy entire planets, just watch starwars and you can see her in the deathstar.
The Good Doctor.