Why is Elise a Tank in the Current Meta?

Elise is a champion who is currently forced to build tank to survive the game. To me this makes very little sense, she's a spider not the hardest of things to kill but something that will kill you very quickly. To me this sounds more like an assassin than a tank and according to Riots champion release she was designed with being a partial assassin in mind, not a weird tanky fighter thing.

Elise does not get enough of a benefit out of building AP, Her ratios are super low for a champ who is meant to be a mage/assassin. Even if you use her current in game classification of mage/fighter that doesn't answer why the hell she often rushes a juggernaut enchant into rand's/locket. The other two champs tagged mage/fighter (swain/ryze) tend to rush for ROA and AAS, Swain also builds into late game AP. The champion tagged mage/tank (vlad) builds early WotA most of the time, into late game AP. The most AP that Elise tends to build is a Rylai's and a Liandry's.

So Elise isn't fitting her theme at all. What is the solution to this problem? The first and simplest thing you can do is to buff Elise's ratios and return at least some of her spider form armour and MR in spider form at the expense of some base damage.. But honestly Elise is probably far enough gone to justify a minor rework or even a full kit rework.