It's tough to claim any talent is a must-have. Rogues will still do 2/3 of their regular attack damage w/o Backstab, and all Scoundrel abilities that result in a guaranteed Backstab will still Crit even without the talent, and those Rogues wouldn't have to get behind their targets and would enjoy the benefits of another useful talent, such as Warlord of Pawn.
What one can say, is that they must have Backstab to have theoretical competitive DPS with Str-based melee classes. But a lower-damage class with greater utility can still be a viable alternative.
