The Thief is easily the squishiest class. I would expect Elementalist to do better in PvE.
The Elementalist has an awful lot of defensive, healing and control spells. Surely, the class runs more of those spells at once than any other class in the game. Look at the focus: complete projectile denial? Oh, and Invulnerability! Insane! No question, a skilled Elementalist can Blind, Knockdown, Vulnerable, Cripple and Chill everything they look at, all at once. Trouble is, they do not have a lot of options for damage on a sceptre, staff or focus (dagger seems to have all our offensive spells). This results in either a close-range glass-canon, or a mid- or long-range control-heavy character who has less offensive options than other classes. More of those options are AoE than other classes, but they have less.
I have a Ranger, an Elementalist, a Thief, a Warrior and a Mesmer. The Elementalist, in my opinion, does not have the highest learning curve. I honestly think many players puff it up more than it is. Our attunements are more obvious than weapon swapping for other classes, because they have clear, defined roles and are already determined for us. The Elementalist is not the squishiest, the Thief is. The Elementalist does, however, take the most effort to play. I feel mentally exhausted playing the Elementalist, whereas the other four I can faceroll PvE. It also takes me more hours to attain the same progress compared to the other classes. Elementalists are perfectly viable, but, as many others have said before me, they take more time and effort to attain the same result at the other classes.
From what I’ve read I understand that Thief is your main? Back on topic: I don’t think you understand the elementalist very well. The only way you’re gonna get acces to Invulnerability is if they give up on alot of great AoE abilities. In you’re post you give the impression that we have acces to all these abilities the entire time. I disagree with the statement that Elementalist don’t have the toughest learning curve in GW 2. If you disagree with me, I would like you to specify what class would be harder to learn and why. I’m not a single minded person, so please do share your opinion. There is also a something you forgot to adress in while you were claiming that Thief was the squishiest class right know. I do agree that thieves hardly have any good damage migation abilities. I do however not agree that this makes them easier to kill. Stealth being the obvious reason, but if you disagree on this point please do share your opinion on it. Last point I wanted to adress was that you claimed that Elementalists are viable. I strongly agree with you on this point. Elementalists do require more work to achieve the same things other classes do with little effort, I however think this is also the part of the charm. It makes bosses that warriors just slash away at far more rewarding to kill as a elementalist.
This is my opinion and therefore it will most likely differ from alot of people.
However, if good arguments are made opinions can change, so please try to keep discussions civilised.