Unfortunately, champion "balancing" isn't as simple and easy to do as you'd expect. It takes TIME because riot has to base their changes on statistics. If a champion is being heavily picked and has a high win rate, they need to come up with a solution and even then, they can't gauge if that solution is enough to fix the champ so that means waiting for more statistics from that champion once these changes release in order to decide if it needs more tweaking.
ALSO, there are many champions out there that we don't know are OP yet. Its due to the meta and popularity of certain champions that we can kind of guage whether they're broken or not. We have no idea what the potential is for some of these underplayed champions. Also, theres the issue of certain items/builds having a huge impact on a champion's success. We don't know what they are until some player tries it and makes it public.
Sorry but I doubt riot is capable of fixing all the problems in the game within a few patches. It takes time and I'd rather have them working on something else other than sitting around, twiddling their thumbs and waiting for the statistics to roll in.
I personally think riot should focus on improving their client and server stability; stuff that we know needs immediate improvement and can easily be fixed.