ad - basic attacks, attack damage modifiers
ap - ability power modifiers
ad and ap do not directly translate into physical and magical damage. nor do they directly translate into aoe, ranged, melee, etc.
in fact it's a bit silly to try to compare the items based on what role uses them because simply put at least 1 champion in each role can use the item. that's the benefit of having a large and diverse roster.
for thematic purposes i'd argue that each item was thought of as an item to answer a specific situation and not so much about "do we have one of these"
i've listed most if not all of the "defensive items" below with at least 1 unique scenario.
TLDR each item serves a purpose regardless of stats provided. copy pasting items and then swapping out stats isn't necessarily a healthy alternative.
- made for assassins with long cooldowns to catch opponents off guard by performing 2 burst chains without retaliation
- made for mage vs mage combat
- meant for disruption based champions to control front lines
- designed to throw an opponent off by granting a shield that wasnt expected. contests burst damage.
- free a trapped champion from entanglement during engagement or retreat.
- meant to be used by high hp/base ad champions to block shots. direct counter to caitlyn's R among other things.
- designed as a reward for champions with deep wells of mana for their struggle early game. meant to aid a champion by allowing them to flush their mana reserve and use it as a shield since their damage is usually DOT effects. this grants a more immediate benefit to counter shear damage output.
- designed for hit and run tactics.
- meant to prevent getting locked down as an assassin going for the back line. ineffective due to the cost and limited effect.
- anti basic attack aura. works well against melee attackers who rely on basic attacks to apply debuffs or grant buffs.
- creates an amplified zone for magic damage. on its own is very ineffective unless used by champions with DOT auras such as karthus or mundo. main benefit is the magic resist which is better on other items. replaces rod of ages in most builds.
- designed specifically for old liandry's + teemo shroom/cassiopeoia. DOT counter.
- creates a minion that requires the enemy champion to deal physical damage to it in order to defeat it. great for afk pushing lanes or countering aggressive mages.
- grants the defeated player 1 more chance at killing their opponent. useful for high skill based champions or lifesteal builds where your opponent has applied grievous wounds to you.
- for champions with little impact in their abilities, but can spam them consistently. meant for tanks with low cooldowns or fighters with high basic attack damage and not enough lockdown.
- meant to be used to counter heavy aoe attacks like zigg's R.
- for saving your tank (or dumb friend) after they've been crowd controlled.
- a do it all answer for critical damage users - ashe, yasuo, jhin etc.
- meant to be an item used for contesting epic camps, preventing escapes, and rushing vulnerable turrets with baron buff.
- for champions who need to stay in lane or are almost impossible to kill with burst damage.
- for split pushing.
- for champion duo lanes that rely on a lot of teamwork (xayah and rakan, taric and kalista, etc.)
- useful for fighting older camps that used to deal magic damage.(baron, dragon) now used to whittle down magic tanks while dealing lots of on hit damage.
- punishes classic lifesteal. counters high attack speed users.
- creates a do not approach zone. useful for farming. must have on champions who do not prefer to engage their opponents in lane.
- buffs heals. useful on self healers or if your team has a soraka/sona. almost a waste if the enemy team buys grievous wounds.
- prevents hard crowd control
- meant for divers or to combo with mighty blow. underappreciated.
- anti-basic attacker. works against all enemies whether you're in lane or jungle.
- reduces slows.
- mainly prevents duelers from out damaging you in 1v1's.