It is interesting that Horford and Grant are +16 in 43 min (Grant has total 155 min) in a variety of line ups (+10, 21 min in the 4th qtr). Brogdon has not been great so far with the starters. Not bad, just kind of neutral. Grant is playing 28% of his total minutes with Horford so they are using that pairing a fair amount, just not to start the game.
What I see subjectively is that Brogdon has the ball in his hands a lot. He operates with high Usage%. There is more opportunity for that with the second unit. That kind of offensive punch was what was missing from the bench last season in the playoffs. Maybe Brogdon can get a few more minutes but I don't see Brogdon starting. Adding punch to bench line ups is the role they got him for. He is doing that.
I wouldn't give on Smart as a starter just yet. That was an awesome starting unit last season with him as the PG, but with RWill in the mix of course. And the starters (with White) have been good so far this season, +17 in 88 minutes (Smart and White were not great together last season).
Seems they are still experimenting with line ups, especially around the bench. Vonleh and Griffin were playing more earlier in the season, now we are seeing more of Hauser and Kornet. If you aren't going to play Vonleh and Griffin, it is hard to start Grant. There is no one to play with the bench. I see that is the key to being able to start Grant and Horford, you need something from Griffin or Vonleh or both.