You need better batsmen.
At theoretical full strength you have a test standard team (Watling, Flynn, Williamson, Styris, Marshall, Vettori, McGlashan, Aldridge, Southee, Boult, Arnel) but that's never going to happen nowadays. Last season Williamson and (randomly) Yovich were all that were standing between success and failure with the bat.
Good FC players are hard to find, hence every domestic side is a bit weak if 2/3 of its best players are injured or playing for NZ, but ND don't appear to have the backup batting quality that CD/Auckland and to an extent Wellington do (Wellington has 10,000 players who all seem to score 30s).