I think the core issue is more that hardcore optimization boards often fail to understand that you can have advantages outside your "main role".The core issue with 4e's Vampire is that it is a class on which they used all their design hours coming up with a custom healing dynamic to make the class extra durable but then forgot to make it a defender.
Also a vampire fits a lot better to be a striker than a defender especially with this mechanic, since a defender can lose potentially several healing surges in a fight if the defender manages to really make the enemies focus on them.
In the end 4E combat is about losing the least amount of healing surges. Strikers help by killing enemies faster. But if one has a defender which has slightly lower damage, but uses themselves less healing surges than normal, thats perfectly good for the team.
A cooperative team game, even if it has roles, still is flexible, and its about working well together in a team, its not about whiteroom situations. A vampire being a striker which can take quite a bit of beating (similar to the barbarian) is a plus.

