Riot (and everyone, really) has always had issue with balancing resources, skill, risk and reward. So much so that they've virtually cut out resources as a balancing point. So much so that "higher skill" needs to be homogenised with 'less skill' with similar or virtually non-existent reward difference. Less skill, less resources, less risk champions will always be preferred if they have a skewed reward. Those with more strenuous restrictions in non-reward areas while having excellent rewards that are circumventable are eventually "found" then homogenised. Many get their resource supply buffed and then get everything else about them nerfed in subsequent patches.
Some champions have been lucky and have averted issues forever as their "restrictions" were hard to overcome. Season 3 items are a really interesting curve ball in balance. Lux/Nidalee/Teemo have always wanted capped CDR and would struggle to maintain the power curve required to compete while achieving it, not anymore. Lux, like many champions have always been in the "not allowed to actually be good, otherwise they're too good" pile (Mordekeiser, Shaco, Ezreal, Nidalee, Talon, Eve, Xin, Tryndamere, Warwick, Zilean, Shen, Rammus, etc etc), basically any champion who once they actually feel "good" to use are already in overpowered status. Once those champions are all in nerfed-ville, it returns back to the characters who just have better move sets than everyone else (Jarvan, Irelia, Orianna, Lee Sin, Anivia) or just bonkers laning with reasonable transition (Renekton, Riven, Garen) dominating and the cyclical nerf roundabout continues.
So, I think what you want to be looking at is that Lux has an abusable characteristic which has seen considerable balance changes over her history (remember when she used to do moar damage then they were like "oh, uhh, we like her being supporty instead, tehehe) which resulted damage nerfs just as she was starting to see competitive play, if she had easy CDR back prior to that, she would've already been an A+ carry. A lot of characters have power spikes from specific items/stat preferences and right now CDR for APs who "hard-scale" with CDR is a problem as it's too good/easy/cheap a build path. Other characters who spike at rylais or zhonyas are at a build path disadvantage, and it's really starting to show. On top of that, those which use rylais/zhonyas primarily are ones which are 'closer' to the action than other build paths, but poke/stall is too common right now as nothing else is viable enough to survive.
So in other words,
Lux/Teemo have abuse mechanics which are easier to achieve now than ever before. On top of that, everyone is too ****ing squishie to afford to be anywhere within 500, no 600 no 1000 range you need to be away from every character these days lest you get ****ing one shot.
tl;dr The characters with 1000+ range are the best right now. Especially if they're AP and especially if they like 40% CDR.