Its pretty obvious Dennis Schroder is just not anywhere near as good as Jeff Teague in the half court. That has been the Hawks biggest problem. Nobody respects his jump shot so defenders just stick with Dwight in the PnR and sag off Schroder.
Also, they have no secondary play maker with Millsap out, and the wings (Korver, Bazemore, Sefalosha) have been mediocre at best, and much worse than in seasons past. Not much bench help either outside of Hardaway Jr and Muscala, who have both been "just ok".
Lazy people will blame Dwight because he's the easy target, and people don't like him, but he hasn't really been the problem at all. I mean, they obviously miss Horford's passing and shooting, but I think it's been a pretty even trade off in what they've gained in rebounding and paint presence.