The huge hit to Vitality is a major downside to Glass Cannon that I feel does compensate for the AP boost it gives. A character with it ends up having to go far more heavily into Constitution than would otherwise be necessary at the expense of simply having a higher Speed. Higher Speed improves a lot of other things - including initiative and first-turn APs, which will often make or break the party in a serious battle.
Yes, you can use Lone Wolf to partly offset the loss, but it must be understood that Lone Wolf is an overall power decrease for the party. Two characters are stronger than a slightly-better single one, especially once CC becomes commonplace. In multiplayer it does have some convenience value since it reduces the amount of waiting and management a person has to do, and people might be drawn to take it for that reason, but it still comes at the expense of overall power.
