There is no top four. There's a top three.
Dante Exum is not worth trading the sixth pick plus other assets for. I am absolutely convinced that there are going to be a number of players in this draft picked after him who end up with considerably better pro careers.
We just need Danny to pick the right guys.
And I disagree with you entirely.
After Exum the next vest guard in the draft is Smart, and there is really no benefit (skill or physically) that Smart has over Exum. Exum is far superior athletically, has similar defensive ability, has similar scoring ability, has the same wealness with his jump shot, but has far superior PG skills (passing, court vision, ball handling) and is both quicker (benefit at PG) and bigger (benefit at SG).
The only other guy you could argue is on par is Vonleh. Nobody else outside top three is a threat on both ends of the court.