I'm not so much worried about Horford as the team in general. if Brown, Hayward and Tatum were playing at last year's levels (and for Hayward, his level of 2 years ago), Al would be THE all important glue guy in the starting line-up --> doing all the small things that are needed for great teams to win.
with the offensive struggles of the starting line-up, the 'glue' he provides isn't what the team needs which is star production so his lack of numbers is more glaring