Posting here the post of Glory ln Death (NA) (give a medal to this man, he sums it up greatly)
Every position except Bot has multiple viable classes that normally fill it.
Support has Enchanters/Catchers, Tanks, and Mages.
Mid has Assassins and Mages.
Top has Divers, Skirmishers, Tanks, and Battle Mages.
Jungle has Divers, Assassins, Tanks, etc.
Bot has Marksmen.
Not only that, but Marksmen go to literally every other position. Why is it a problem when Ziggs Bot has under a 5% pick rate? Marksmen should not have a monopoly on the Bot position. Just because other champions can viable be played there does not mean Marksmen are weak. It means that they aren't oppressively strong.