If I may, allow me to join this argument. There are two things I wish to bring up: your earlier comment about LeBlanc countering Ahri, which will be the topic of countering in general, and the title of the board. I will start with former.
Before I begin, I want you to think what does the term 'countering' mean in League of Legends. There are a few variations of this term but the primary two are kit dominance and kit superiority.
Kit Superiority is due to the stats of two champions, where one seemingly comes out on top. An example is Caitlyn versus Vayne. Caitlyn has the longest base auto attack range in the game versus Vayne, from what is hear, is on the shorter range side of marksmens. From this, Caitlyn would "counter" Vayne as Vayne would have the hardest time ever getting to her. Caitlyn, if played well, can remain in a safe position and always pursue or retreat from Vayne and defeat her just from the stat of their ranges (and other abilities). The only problem with this "counter" is that the player- key word is player, not Vayne- can out perform Caitlyn from knowing how she works as a champion and can use their knowledge to deal with her. This is why in higher elo the term "counters" is not used because knowledge is powerful and knowing how to deal with a champion, regardless of stats, can make it a fair game. This is why Caitlyn is known to be a lane bully in bot lane, due to her superior range. This is not a counter, this is lack of knowledge of how to deal with that champion.
Kit Dominance, in contrast, is the actual kit of a champion can give specific champions a nightmare to deal with. Example: Cassiopeia versus Yasuo. Cassiopeia's Miasma (w) grounds enemies and cannot use movement abilities while inside. This is a counter to Yasuo as he cannot use his .5 second to .1 second dash while in the ability (and probably even his ultimate. as he does go to the target from wherever he is. but I do not have confirmation about Yasuo's Last Breath so I want to merely mention it) and forces him to use less abilities than he could otherwise. This type of dominance in the nature of their kits results in the most experienced Yasuo players being annoyed at the fact that they cannot dash (and for this example, we will say he cannot use his ultimate either) and could result in death or lost kills, especially if the Cassiopeia player knows what she is doing and can use her Miasma at very well times. This an actual "counter" unlike your statement about LeBlanc countering Ahri.
LeBlanc is a burst Assassin (Primary) Mage (Secondary). She gives most, if not all, mid lane mages a hard time. Ahri herself does not have a terribly hard time dealing with her than most other mid lane mages. She is just as annoyed with LeBlanc's all in burst and quick disengage abilities like every other mid lane mage. (Can't wait to see how the rework goes with her! [Sarcasm]). I do not mean to insult you with the following but you are not smart enough (Please do not take it to heart, or at all) to know how LeBlanc works (Season 6 now, Pre-Season 7 soon) to know how to deal with her. Know how LeBlanc works and come up with game plans or strategies on how to deal with her specifically when she appears in your lane.
Know what countering means and know how it works. LeBlanc gives mid lane mages a hard day as a whole; Cassiopeia can destroy a good Yauso player (Presumably if the Cassiopeia player is indeed good herself and know how Yasuo operates as a champion). There is a difference between Superiority and Dominance with their Kits. You will have to learn how to deal with Caitlyn's longer range, but once you do, you don't have to deal with her nonsense. Yasuo will forever hate Miasma and hate that snake.
