Biggest problem with Fire/Dragon:
Resists: Fire (x4), Electric, Grass (x4), Bug, Steel
Neutral: Water, Normal, Ice, Fight, Poison, Flying, Psychic, Ghost, Dark
Weak: Ground, Rock, Dragon (All x2)
Most non-Uber Dragons have a x4 weakness in there. This guy doesn't. If he had stats at all comparable to Garchomp, Dragonite, or Salamence and had those Resistances he'd be bound for the Uber categoy.
*Coughkingdracough*.
Also it would be weak to Ground, and Heaps of things have ground attacks. It is also Weak to SR, so it couldn't switch in Alot. Mabye with a spread like:
70/100/70/110/70/90 It would work.
Steel Dragon is barely worth mentioning. The resistances on that typing are just outstanding. The only weaknesses are Fight and Ground with Dragon, Ice, and Fire hitting neutral. The rest are all resists. Ugh. With any worthwhile statline or move pool that thing is heading off to Ubers.
Bronzong?
Resistances:
Normal, Grass, Ice, Flying, Rock, Dragon, Steel, Psychic (x4), Ground (Levitate)
Neutral:
Water, Electric, Fight, Bug, Ghost, Dark
Weak:
Fire
Bronzong has only 1 weakness, and has a worthwhile statline for a wall. At least Steel/Dragon has 2 weaks that are commonly seen in OU (Ground, Fighting) So it would balance it out.
EDIT: Without a x4 Weakness, most Dragons end up living in Uber Land. The best chance for a new Dragon Type is Grass/Dragon.
*coughkingdracough*
Also most dragons in ubers are there because they have a high BST or mean Attacking stats (Rayquaza, Lati twins, Palkia), Mean defencive stats (Giratina) or both (Draco plate Arceus, Dialgia)