It's not about hp/defenses, though that's yet another thing warriors are better at. DW warriors just do flat out more damage without the need for backstab, and they have better attack skills besides.
If you think that's bad now, things will get even worse for the Rogue in D:OS 2, when the action point system is revamped so that all characters get 3-4 AP a turn, no matter what stats they have, and all actions take 1 AP (except maybe daggers will attack twice).
