Hearthpwn

From my experience over the last month, depending on your lobby, you have to skip the midgame entirely.

You need an endgame build (or the ingredients for one) by turn 9-10. If it doesn't work because you get crappy triple rewards (or no triples) or take too much damage, you get 6th place at best, but if you try to play more conservatively, you won't do better than 5th either.

Simply because there are a handful of heroes (Omu, Y'Shaarj, Elise, oftentimes Patches...) that can powerlevel while taking litte damage, or potentially inflicting a lot of it, you have to do the same somehow and hope you won't die. When half your lobby skips the midgame, you usually can't dwell on it. When you take 15+ damage from Ghastcoilers, Tide Razors etc. while you are still on 4, it's usually over. 

A few heroes like Ragnaros can potentially afford to level a bit slower and build up something in the midgame with a lot of scaling. With Tess, you can sometimes get a perfect steal, allowing you to put more emphasis on the midgame. With Geoge you can stabilize better, if your board scales well. But generally, you can't stay on 3 or 4, and Dragons, as others have said already, don't have much power at that point either. 

To do well with Dragons you pretty much need to race to 5 with a triple and get Kalecgos. And Nedina a bit later to seal the deal (though other builds sometimes outscale you).

Last time I got first place with Dragons, I was taking 20-something damage while freezing a triple from 2 all the way to 5 as Reno. I got Kelecgos, I turned it golden, and even though my dragons were actually pretty crappy (no Bronze Wardens), it was enough to stabilize and crush the rest. It sounds like a crazy highroll, but you need to get crazy highrolls these days anyway. Might as well go for it.