OK, a quick stat compare of Smart to Brunson:
Smart Brunson
FG% 34.9% 50.0%
3P% 30.5% 32.5%
Reb 4.8 3.8
Asst 5.3 5.5
+/- +3.6 +2.4
NetR 4.8 3.6
AssR 28.4% 26.2%
Pace 99.0 96.4
Use% 16.9% 21.9%
TORatio 11.0 8.1
EFG% 46.6% 53.8%
Smart is actually better at +/-, Net Rating, assists (ratio), pace, rebs, on less usage. Brunson gives you better shooting (although not much better 3P%), fewer turnovers. Smart is 6'-4", 27 years, Brunson 6'-1", 25 years. Smart is also far more versatile, particularly on defense, and brings significant other intangibles.
I predict you are not going to see a big deal made to get Brunson. Further, if Brunson gets paid $80M, I hope it is not the Celtics.
I feel Brunson is a decent player, we just don't need him. Yes, his shooting numbers are better than Smart's, that would be nice to have in a PG and maybe he turns into a IT and gets really good late in his career. I am not seeing it though.