I don't know hot it is about SDMG - IMO it's pretty powerful, but nothing special, just machinegun. Name is good, but it's sprite sucks.
If we get to the celebration... IMO it's far too weak to be ML drop. The same goes for Snowman Cannon. For other classes, ML drops thing that - even if joke like Meowmere - are super destructive. We have fishgun (pretty strong, but still joke) and lame, weak, damned firework that has slow firerate, low damage (as for endgame weapon) and is far weaker than it's "predecessor", the Snowman Cannon.
And both of them are jokes! We have no badass, cool weapons, just jokes. Even if SDMG is strong, it's joke. Celebration is damned, weak and sucks. And it's joke. We have no serious endgame weaponry, VB and Phantasm being nerfed constantly because of being not ML drops, while only weapon that could match in power other classes' endgames being SDMG.
So, we have low damage. If we have high damage, then no movement = instadeath. We have only one powerful endgame weapon, being also our only ML drop, but it's fishgun. (Yeah, I know that we have theoretically two ML drops. But what, did You count Celebration? It's a joke, but not on game - on players. Broken as heck, and really not worthy to waste ammo using it.)