Out of curiosity, I tried Triple Trio and the Tree, without changing difficulty mode (despite never having completed it above Normal in my 1H era) from Nintendo.
It was surprisingly easy.
Monsters never ever managed to trigger Spark of Life (completely different from Arena or Random Encounter experiences), and while I did use some spirit draughts for safety, maybe I would never have reached the point where SoL would have gotten disabled.
It was also quite easy to keep high mp.
And finally, despite the battle going the worst possible way from a tactical point of view (Yggdrasill die first, then the 3 goddess follow, thus giving monster the boosts that come from that for the highest possible duration), I never felt any danger.
I probably would not go as far as thinking that it would be ok to try PFUDOR (as the gap between IWBTH and PFUDOR is completely different compared to other gaps between difficulties), but IWBTH would be possible, though it take far too much time.
Finally, got a
Exquisite Shade Breastplate of the Fleet as reward (in addition to the various trophies), not really great considering it's the rarest type of battle (I hadn't played a RoB for years, yet I only have around 30 token of bloods)