Why mages get to have defense but adcs don't

Ranged characters always make a tradeoff: By being allowed an advantage of dealing damage at a distance, they are at a disadvantage at close quarters combat.

Champions like mages who deal burst damages have windows of power and weakness from their cooldowns meaning they are always looking for openings to dump combos, while adcs who deal consistent damage have more of a stream of damage meaning they are more so looking for better positioning so as to continue dealing damage without creating said openings for enemies.

The reason mages get to build defense is those windows of weakness. Many mages can't do much damage at all once the rotation goes off, giving you a chance to punish them uncontested. An adc though always deals damage, and does not present such windows without letting themselves step into a bad position.

Tldr; the nature of mage combos relying on cool downs leaves you open more often

Sorry for typos, my auto correct works double duty