If half of his selling points to you is that his one STAB move anyone has talked about hits harder, and already OHKO's everything of that typing aside from AV Goodra, and you still think he isn't quite good enough; please just stop even reading this thread. He has more than enough to deal with many 'mons out there, he has is problems doing so is usually the issue. Adaptability won't fix his speed tier, nor will choice specs (or even scarf for christ's sake) do anything to fix it. Look at his positives, then compare them to the negative. You know, like Smogon used to do before everyone coming to this site instantly thought they were the bee's knees.
Dragalge needs rather hefty support to do any critical damage to an enemy team. Adaptability allows him to rend even bigger holes on what switches he does force, although that number will be few and far between. You'll see him around, and he will be packing a standard movepool of Dragon (Pulse/Meteor)/ Sludge Bomb / Thunderbolt / Scald or whatever else someone may want to add to him for coverage. On top of that, he can take a few hits before he departs. I definitely see his usage rising, although he may consider himself lucky to break into even the C tier.