I’ll anecdotally say that my Mesmer often has 3 clones up all the time - for instance, when fighting in a dungeon, I can get up 3 phantasms and for the most part, they’ll only go away when I blow them up. I use staff + greatsword, typically starting with staff, so I pop out a phantams and a clone fast. Throw down chaos storm, swap to GS, put out a beserker, and then when the cooldown is up, swap back to staff for another phantasm (alternatively, I was using Phantasmal Disenchanter as a utility, so I could pop out a 3rd phantasm fast).
Of course, that’s in dungeons and/or in group events. When solo, yeah, the phantasms or clones often get popped pretty fast. However, you have to think that whenever the mob is killing them, he’s not killing you.
And don’t forget, not only can you blow up your clones for damage, but you can get a nice daze out of F3, and some distortion on demand with F4. Plus confusion on F2 (which I don’t ever use).
I’ve also got the trait where I summon a clone on a dodge, so in reality, I can get a clone and a phantasm up with staff, dodge to get a 3rd, blow them up, swap weapons, and do it all over again with greatsword.
I’ve played a lot of Mesmer. And even when I go to other classes and play them a while, I always come back to the Mesmer. The Mesmer doesn’t kill terribly fast, but whenever I’m playing him I feel I can take on anything. Whereas with my Ranger or Engineer, when I throw a bunch of damage at the mob and it’s still alive, I sort of feel I’m out of tricks (I like those other classes, but the Mesmer just feels like he’s got a bag of tricks compared to the other guys). Plus in WvW, I use Feedback and Null Field to provide a lot of functionality.
As for AoE on the Mesmer, there’s Chaos Storm of course, but I also picked an Asura for a second AoE, Radiation Field.