Why are people always so illogical about champs they hate? That's pretty funny.
Ahri has low mana costs? I'm sorry, but expending 75 mana a Q at lvl 4 with around 447 mana is NOT "low" mana costs. She has moderately high mana, and exploding her full QWE combo at lvl 4/5 takes her to under 50% mana. She can legit only do that combo twice in lane before going oom. Therefore, Ahri's are mostly with only using Q or W once every 15-30 seconds or so in the starting of laning phase. If they're blowing spells at a faster rate than that, they're going to run oom fairly quickly.
If you get whittled down so much, that by 6, she can all in you -- that's your fault.
Very low cool downs? Lmfao. She has a static 12 second CD on E before CDR. Max CDR, Ahri's Q is on a FIVE second CD, her W (being the shortest CD at 3 seconds -- though you have to use it first) and her E is on a 8 second CD. I bet that's pretty low for "kite mage" status :

A huge mana pool? Her mana pool is moderately average when compared to every champion: http://leagueoflegends.wikia.com/wiki/List_of_champions'_mana
Negligible sustain that really is rarely EVER noticeable? She has to cast around 3 abilities (around 120-180 mana early) to get her passive, THEN burn her ability again (another 75/40 mana) to get her passive. Yeah, that's good over a decent amount of time (think 1.5-3mins)
Massive movement speed that decays FAIRLY quickly. Though I can admit, if you're playing someone who doesn't have any gap closers, that movement speed can be REALLY annoying. I wouldn't mind if they made it to where you had to hit a champion to gain that movement speed.
And a crowd control that can be body blocked by allies and minions alike and only affect one person? Might as well complain about every freaking mage in the game:

I mean, need I continue about how even adding that to your list was completely and utterly pointless? And overloaded? Really? She has one of the most cohesive kits in the game without going overboard. You call one tacked on MS buff that made Ahri go from garbage to viable overloaded? They just need to make it more situational to make her less annoying to kill. However, she's a fully skill based champ that can very EASILY mess up her entire combo.
Her kill pressure, compared to most other mages, is also really low and her biggest spike is mid game. She's not going to carry a game come late game, she can be ran down fairly easily by most champs, susceptible to flanks as well -- but you want to lower her 60 CD ulti when every assassin in the game has about a 60 CD OR LOWER cooldown on their ultis? Yeah, how about no? She needs something up just as often as everyone else trying to kill her. She's more useless without her ulti than some other champs are. She can only throw out her Q or her very linear E to try and affect a teamfight when her ultimate is on CD.
Even though Ahri is my 2nd favorite Champ next to Riven, I'm being completely objective here. If you think her kit isn't balanced, then maybe YOU'RE the one we need to be worried about. She's a burst related kite mage with less DPS than almost the entire mage class. If you play Ahri, you'll feel the difference in how much harder you have to work for kills over other champs. Being a person that spammed almost 130 games for ranked alone using Ahri last season, let me tell you how good I feel when I can just melt people at lvl 4/5 playing people like Annie, Syndra, Viktor etc and going "HOLY DAMAGE".
Only way Ahri is doing that much damage, is if you let her get fed. I can 1 shot ADCs at lvl 6 on Viktor from full health with my 2 dorans and E upgrade. Just because Ahri runs bot and 1 shots your 50% HP adc and support, doesn't make her OP.