In early beta, the mage suffered. Back then, I got so frustrated I switched to Templar and used it much like I would a mage (Didn't bother with healing). That worked out quite well.

Shortly before launch, the mage was strengthened. I've made two mages these two days of early access and both seem to be doing fine. Maybe you are using the wrong elf? Wood Elf would do well as Nightblade and Dark Elf as Dragonknight or Nightblade, I guess. High Elf is made for Mage.

I've also had success with Nightblade/heavy armor but not with starting with a bow. Adding bow as a second weapon (dual wielding blades for first) worked well, but if I tried a bow first Nightblade (and I tried it with a Wood Elf who has an affinity for bow), the poor thing just couldn't survive. My Khajiit Nightblade, on the other hand, who started with blades and added a bow at level 15 did quite well.

There are a couple of threads that discuss Nightblade in a lot of detail. Go check them out.