It's not that . . . it's that is is the obligation of the casters (arcanes, divines, rangers and pallies for resists, etc . . .) to provide certain buffs to the party. If you can do that without extend it's all good.
Expecting people to be 100% self-buffing is absurd (and 3 of my 4 toons are self-buffing).
I'm keeping extend because it lets me be lazier and not have to rebuff people as often.