Not all AP mids can actually carry without snowballing. Ahri, Katarina, Cassiopeia, Azir, Karthus or Ziggs can solo carry with farm alone while Annie or Malzahar are unlikely to solo carry if they don't snowball and put the enemy team behind.
Not all ADCs can solo carry without snowballing and suppressing the enemy ADC. Sivir, Vayne and Kog can carry even if they're 0-20, as long as they get items. Lucian can't solo carry when both ADCs are 6 slotted; he has to end the game before the enemy ADC can get farmed.
Not all bruisers are incapable of solo carrying. Jax is the most infamous solo carrying bruiser.
I think whether a champ can actually carry is an important distinction to make.