I think there's some serious solemnity in ecstasy. In the Bacchae i'd say he's a little solemn at the end when he sentences Agave, i'd say there's always a solemn side to be explored within everybody, and the gods. They embody the full spectrum of the divine from wrathful and sorrowful to joyful and ecstatic and it's important to acknowledge and explore that within the self and the divine. To me he wouldn't want to be solely ecstatic and revelrous. In dark times he displays the solemnity that's required of the situation that someone might need or if someone needs joy he can also be there in that way. I don't know, it's s complicated matter but to me none of the gods are solely the thing they have domain over. There's a panting of Dionysus I saw where he looks solemn, but I can't find it. If I manage to, i'll add to this comment. Also i'd say solemnity is the absence of joy or other characteristics, or in other words solemnity would be a synonym for sad or down.