Well, yea?
They are all AD items that give good offence and defense as well and I stated AD items, not ADC items. No-one's buying these items for the offence but the defense (except Va(a)rus/Kog'maw and the Wit's End and Draven with the BT, but that's an exception), everyone gets those items for the defense they give.
Like it or not, that's the case, AP champs have 2 defensive items while AD dudes have 8, not counting many more that can be abused by them (Frozen Mallet is still on Ez's buy list, while for a while it was used by a lot of ADCs). Yasuo, Zed, Lucian, Kayn, Lee, what not that's AD want to go defensive items? Well, they have BT, Maw, DD, GA as 4 strong items. Yea, noone will buy all 4, but then again, even if they do, they get a stupid amount of defense and don't lose much offense unless they are crit champs, but even then, they can safely go 3 of these 4 after selling boots. All of the 8 items work quite well vs both AP and AD, GA gives armor so it's better vs AD but the 2nd life is good vs both, while after Maw triggers, which more often than not will unless you're against a full AD team, and even then it has some chances to trigger thanks to Smites/mixed damage and such, the Lifeline passive is lifesteal off of all your damage so it doesn't matter what the enemy deals after the passive is triggered.
Vlad and Rumble, 2 AP bruisers go into tank defensive items for a reason, there are no AP defensive items worth a damn except Zhonya, which is already 50% of the AP defensive items.
Any other AP wanting to go defensive? Well, after Zhonya, they either go tank items for little to no benefit but they have no other choice if they want defense, or say "Shaco it" and go more damage and hope they kill faster than they are killed.
Which was my point, you can nerf mages, go ahead, but also nerf AD defensive items. Or give mages more defensive items, afterall, they lost 2 defensive items in Abyss Scepter and GA, so hey, they can get some items as well.