May I ask what you think about Duraludon's viability? :o
Personally, I don't see it having much success in Singles despite having an amazing type combo. Its special defense is poor, it can easily die to STAB special moves, especially if they are boosted by items or moves like Calm Mind or if entry hazards are on the field.
I'd argue it's much better in VGC where you can resort to Tailwind or Trick Room to support it. That way, you can invest in its bulk. and if you chose to gigamax it, it can fire off its steel signature move without any repercussions. Though, steel isn't a great offensive type to begin with.
Also, you can make your opponent despair with Intimidate and a berry like Figy berry.
I can definitely see it having an amazing movepool, like Ice Beam, Thunderbolt, or Flamethrower. However, if it doesn't get any reliable recovery move, I'd rather use Drampa in singles, which has nice utility and doesn't faint as easily as Duraludon, I think.
On another note, I can see it having a niche in monotype, especially dragon. It's not weak to ice, dragon, and fairy, and if it has access to something like Autotomize or Rock Polish, which it could definitely have it from the looks of it, it could steam roll those teams.