The Hawks are legit. It's more to do with coaching and the team makeup than anything else, which is unlike the rockets that was heavily reliant on two players (TMac and Yao), or a player going on a tremendous hot streak that he has no business having (Jennings with the Pistons, Lin with the Knicks, etc ....).
The Hawks are like a hydra, you cut off one head, and there's still 4 heads, you can't really kill it that easily, and the chances of all of their players struggling at the same time is minimal.
That said, they are heavily dependent on Horford, like GSW is reliant on Bogut. Horford had some health issues, and once he goes, the Hawks have no chance in the playoffs and would become very vulnerable.