I keep seeing these posts that Assassins are balanced....

Based on LolAlytics, the top tier in Mid is Yasuo, Katarina, and Vlad. The Second Tier is Karthus, Fizz, Zed and Talon. The Third Tier is Ahri, Malzahar, Kassadin, Zilean, Ekko, Zoe, and LeBlanc.

So basically, top tier is two assassin-type champions and a mage that has no mana, can become untargetable and is generally considered OP by most players and sees around a 90% pick/ban in pro play over three different lanes.

Second tier consists of three assassins and a mage that can cast spells after dying and is also generally considered OP.

Third Tier is four assassins, two champions that specifically counter assassins, and a mage with mechanics that allow her to deal with assassins and in the hands of a skilled person is pretty close to broken as can be seen in pro play.

Basically, you play assassins or champions that have very strong assassin counter mechanics or you have to be able to become invincible (and still buy Zhonya's in your kit) or you are not really in mid lane at all. Nicely balanced.

On another note, if you notice, the top three champions have no mana. Weird how when you are determined to destroy sustain that this happens? Oh, they also have ridiculous mobility, burst, roaming potential because of wave clear, and various other overloaded mechanics. All of which are the most common complaints about League and the most common thing that drives away new players.