So, this is actually the reason I quit playing mid and started playing adc. I used to main syndra mid and would whomp on anyone but yasuo, but would lose games because my adc or top lane would lose hard. Since I sucked at top lane, I started maining adc. I've climbed quite a bit since then.
Even though I feel your pain, I disagree with you...Because there are AP champs that can 1 shot carry champs. You just have to be good at catching them out and putting your combo on them. Lux is a good champ, but she doesn't compare to champs like veigar, velkoz, or xerath.
Honestly, I was thinking this had something to do with the change in adc's. Where alot more people are taking duo mage bottom lanes opposed to adc and support bot lanes. Mages have good early games when against carries, but horrible late games. Maybe that's why when it comes to winning, carry champs are more viable.