Horford has good team honours in the NBA but lacks top team honours. 1 title and 1 defeated finalist in Boston. Only ever made the Conference Finals once with Atlanta and they were swept. So good teams but not great teams for most of his career. If Horford had of led Atlanta to more Conference Finals, or more Finals, I would have viewed him as a lock. But without it, his team success is a bit lacking.
The guy I want to see in the HoF is Rasheed Wallace.
He made the playoffs every year of his career except one - his rooke season. He made the Conference Finals in 1999 and 2000 with Portland. He made another 5 Conference Finals with Detroit including 1 title and 1 runners up in a 7 game battle. Sheed was a key part of every one of those teams. Then he went to Boston and earned another runners up in a 7 game battle as a key bench player.
That is 8 Conference Finals, 3 NBA Finals, 1 Championship.
Most of those years were 50+ win teams.
That is elite team success. He played an important role in pretty much every Championship run-in from 1999-2010.
I don't think Horford is at that level. His Atlanta teams weren't strong enough.