Let's get this straight: Maw/Steraks/Mercurial are NOT defensive items.
gives 55 Attack damage, 10 armor pen, and the lifegrip passive gives you a heap of other offensive buffs. the shield and mr are just icing on the cake. That makes Maw a good item in every regard, not just defense.
gives a ridiculous amount of base attack damage along with a huge ass shield and some HP. 25 and 25 make 50, so it can give you up to 50% base ad.
75 AD. that's one of the highest in the game. 10% lifesteal and 50% bonus MS when you use the active. the 35 MR and quicksilver passive is again, icing on the cake to make it an item good at everything. Though, it's 3700 gold, that's pretty damn expensive. Bloodthirster gives the same amount of AD as a purely offensive item. Though, I'd argue this one is the most balanced of the 3.
What is the tradeoff for building these items? With Zhonyas, you lose mana, cdr, and it takes a hefty time to build since it's expensive as shit. You trade CDR and mana for buying some armor and an active. Zhonyas is honestly a meh item when you don't factor the active.
With these 3 items, you gain damage/lifesteal/armorpen/movespeed. Building these 3 items along with other AD items and you will not notice a fall off in damage while also having ridiculous survivability.
Anyways, that's my two cents. Maw is getting nerfed though, so I like that.
. Stupidly cheap and can be upgraded into one of the most powerful ad item in the game. This is allow ad champs to stack their defensive steroids and the result is this stupid sustained semi-bruiser ad carry/assasin.
is 3500g for some reason. Remove some gold from bc and move it to 
-2300 with better stats.
etc
for AP champs.
also needs its passive CD reduced to compete. Merc scim's weakness is in its build path. QSS is 50% cost efficient, so until you upgrade merc scim, you give up a lot of stats for that active.
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cuz ezreal started to hurt but ended the game... no deaths for me was like 9/0/18 was grand