Well if you have a weak stomach you will have a weak back!
Stomach muscles should be one of the strongest muscles in the body along with the legs and lower back.
That is the 3 core power muscles. If you had nothing else you should have these.
Stomach muscles help with posture, holding in organs, supporting your back, even breathing (diaphram). I would not neglect these muscles if you have a weak back.
If I had to choose with stiff leg dead lifts or good mornings or even hyper extensions to dead lifts, I would choose dead lifts.
Those are the meat and the others are the gravey.
