This will probably get downvoted into the depths of hell, but that's okay. I want to hear y'alls perspective in the comments.
As we all know, this is a high damage meta. True tanks are rare, as bruisers and assassins are far more viable in the current meta. Things like Dark Harvest and Conqueror are frequently complained about on the boards, but for some reason, people aren't catching on to how **STRONG** AP items are. Check winrates on any site of your choosing. AP champs are meta in top, mid, support, and share ADC with Lucian, Jhin and Kai'sa. Why is this dominance of four positions allowed?
Let's talk about specific AP Items. I'll use Banshees Veil as my examples. This is supposed to be a defensive AP item, so there should be significant damage trade-off when this item is selected. However, banshee's veil gives only 15 less AP than Luden's, the base offensive AP item for most mages; and it gives MORE AP THAN VOID STAFF. On top of this, it gives +60 MR (which is more than ANY tank item gives btw), 10% CDR, and a spell shield. How is that a trade-off?
AP champs need to have more clearcut tradeoffs. If they want to do more damage, they should HAVE to build Void staff or Spellbinder, rather than just having enough damage that they can build "defensively" and still one-shot squishies. Most AP champs already have CC in their kit; giving them the ability to build defensively and still one-shot is just too much.
TL;dr - AP champs don't need to build "offensive" items like void staff or spellbinder because their defensive options like Zhonya's, Liandry's and Banshee's provide enough damage on their own, leading to unhealthy itemization.