No
Due purely to his length, strength, motor and lateral quickness he has the ability to defend a good number of today's Small Forwards - I'd say Harden and Iggy would be about the upper limit in terms of the type of guys Smart could defend effectively on a consistent basis.
Once you get to guys like Joe Johnson, Lebron, Melo, Durant, Paul George, Rudy Gay (etc) those guys are too big and too long for Smart. Even if he could contain their penetration, they can effectively just shoot straight over the top of him.
That Smart at 6'4" can defend guys with Harden/Iggy size is a testament to how impressive a defensive player he is, but lets not get carried away. Smart trying to defend Lebron would be like Crowder trying to defend Anthony Davis or Dwight Howard - just no happening.
This is especially true when you have guys like Rozier / Bradley (both 6'2") and Isaiah Thomas (5'10") at the guard positions.
I'm not one of these 'obsessed with size' guys, but even I will admit that a 5'10" / 6'2" / 6'4" perimeter lineup is just too small.
