Tasteh: Feel hereby corrected - I refer to CC as term for all crowd-affecting skills that have an influence on the opposing teams mobility, dmg, or defence.

LeBlanc, build like beforementioned, provides;
1st - a silence, via ulti on two targets in a matter of seconds,
2nd - the slow / root via her chains, and
3rd - the decreased enemies AS via frozen heart.
If that's not enough CC yet, take a rylais, and distortion will provide you with an AoE slow as well.

So feel free to give it a try, your KDs will still be mentionable, but your team wont have to babysit your *** that much ,)

I gotta say, you were right about LeBlanc being not-so-useful late game. With this build, she does indeed survive for far longer. Although my personal build order deviates slightly from yours (I obtain Mejai's, for example), I have invested more in utility, armor, and magic resist over the past few games and it has worked to great effect. +1

I honestly don't see how this makes her a cc *****. She only has one soft cc skill, her chains, which only slow 20%. In a team fight, this rarely matters. As a result, she seems a lot more like a nuke to me.

Please feel free to correct me; I'm a rather new player, but I have gotten some amazing kdr's with LeBlanc being an AP nuke.