*chuckles*
Well, maybe you are right and frustrated tweens will quit.
However, let me take devil's developer for a moment.
Tweens may, for biological reasons, be forever tied mainly to shooty stabby games. But the young gamers become older gamers. Gamers with substantially more disposable income. Perhaps a richer adversarial system would attract them more.
Maybe not.
It would be interesting to trail something like this, in an experimental fashion, by having a 'Wizard of Oz' setup where players think they are facing a super clever AI, but are actually facing a refereed team of human baddies.