"But funnily, his voice is far more appealing on the Soliel Moon. Strange"
Agreed, again. He doesn't strain it as much on Soleil Moon and lies more in his comfort zone, which makes him sound more at ease and smoother. I hope the rought voice on MTB isn't intentional.
It's mostly the choruses that is ruined (well, almost) by his gravely approach on MTB, the verses sound fine for the most part.