It still has Utsusemi for increased survivability. Beyond level 90 /NIN will be superior to /DNC because /NIN will offer Dual Wield III while /DNC still only gives Dual Wield II. DNC gets Dual Wield III at level 60, so it will never give support jobs that job trait. Keep in mind that Dual Wield III is actually the best increase of all the Dual Wield upgrades, jumping from Dual Wield II's 15% delay reduction to a 25% delay reduction. That's a significant leap in damage over time. By comparison, THF/DNC will be able to use Haste Samba at level 90, which would allow THF to gain 5% haste, so 5% less delay reduction while maintaining less a reduction to TP gained (which while wielding daggers is negligible anyway).

Long story short without the math: DNC has become situationally more useful as a support job to THF than it used to be, allowing THF to fill in as a debuffer and back-up healer utilizing TP in parties without sacrificing damage over time. When they raise the level cap to 90 (at the beginning of September), NIN will once again be king.