Um, that's why they're being changed. They want these champions to feel overwhelming. Sure it's balanced when everyone's at a similar level of power and have role-specific strengths, but it's so much more fun when everyone has a unique strength.
Look at Kog'Maw for the prime example of why Riot changes things and what they aim for when changing them. :) Kog is supposed to feel like artillery. When he is "perfectly balanced," he is just a long range ADC with a poke ulti. Now he's...something else.
So for instance I can foresee Lux getting even more CDR - hello again, 20 second ultimates. They'll balance it out somehow; most likely, she'll get nerfs to her MS, survivability, and overall damage. There is no doubt in my mind that Lux will be able to break the CDR cap somehow. She is THE CDR mage.
I can also foresee Brand getting more combos. His spells are a little boring and reward you mostly for spacing out your abilities to make use of his passive, even though the cool effects and benefits make you want to use all your spells at once. Riot's probably going to reduce the damage on his passive but allow it to stack, add some crazy mechanics to his spells, etc. etc.
Overall Riot has displayed that they want to preserve the "feeling" of these champions so that longtime mains feel more love for their favorite champions, not less. They tested the waters with Karma (different feeling) and noted that people reacted sort of badly to the change. I think they'll be much more considerate towards people who already play those champions (in Meddler(?)'s podcast he noted that he would love to change Nasus and Katarina to be more fun and interesting, but literally can't because their specific playstyles have been carved out. People play those champions for those playstyles. They can't take away Katarina's ultimate or Nasus' Q even if they replaced it with something more fun, interesting, character-related, and unique) - and seek to leave them as whatever players want to see them as.
