I dunno if it's been posted but while having one more weakness, Dragonite has higher defensive stats than a Garchomp, and has multiscale.
If I'm correct, couldn't he be a superphaser? If sleep talk selects whirlwind or dragon tail, he'll phase on his action, and if he's faster, they won't get a chance to move first. Obviously, there's issues with his speed, so I'd need to figure out a spread that can work well without sacrificing bulk.
The other advantage is that it can take a fair amount of damage without getting hurt too badly - I believe that a sp.Atk Starmie can't one-shot it with ice beam (Unless it's got a life orb or choice band, I think), and then gets phased.
Trying to figure out the best pokemon to use for a set like this is quite frustrating! It has to be bulky enough to take hits, quick enough to act before some pokemon, and able to learn two phasing moves.
However, if I have my data wrong for the priority, I fully apologize.