It's similar to my story, although I've got atk- Ninian spending a bit more than 120 orbs. When I think about it, 5% is only 2% more than usual 3% which won't make a huge difference. In real life, if someone tells me that I have 5% chance to win, I'll laugh at his face.
Speaking of Ninian, do you think, Ninian, Nowi, Fae team is a viable option at least in tempest?
I think an all-dragon team is viable anywhere, actually. It's just that you'd need to SI a blue dragon and your Tiki to stand up to their respective anti-dragon weapons. And you'd eventually want to give Lightning Breath+ to everyone who doesn't come with it, which is super expensive.
Nowi or Ninian with TA or Swordbreaker can counter Falchion users.
YTiki with Lightning Breath+ and TA can counter Julia. I imagine ATiki can do it too, but not as well thanks to low speed and res. You could always double up on it with Green Tomebreaker too.
For Tempest, you probably want some sustainability, and Fae can provide that with Renewal. Then Fae herself can be a combat healer with Reciprocal Aid, or one of your other units can pack it.
Actually, it might be better for Arena than Tempest because many good dragon builds are built around tanking and countering, which requires lots of sustain in prolonged fights like in Tempest. I suppose you could build your dragons around initiating to help get around that, though.