As much as I like Brogdon (not to mention Rob and Derrick), Smart is the 3rd member of the 2022-23 Big 3.
Boston is not a big 3, it is disrespectful to both Tatum and Brown to include Smart as anywhere near them.
We all know the Jays are head and shoulders above any other teammate. While it pushes the envelope to include Smart in a Boston Big 3, I sincerely doubt either Jay would feel disrespected by the suggestion that Smart is #3.
In addition to being an emotional leader and averaging 7+ assists, he’s the defending Defensive Player of the Year. Not without a resume.
I agree with Rody that a healthy Rob is a candidate for the third slot. And of course a team doesn’t require an actual Big 3, it’s just an NBA tradition to identify the core 3. Not all that meaningful.