Sanga was a top class batsmen but his record was significantly padded by him filling his boots against the minnows.If you judge strictly by averages then kumar sangakkara is the 2nd best ever (counting only batsman who have made 10,000+ runs). 12,400 runs at an average of 57.40.
By comparison ponting made 13,378 runs at an average of 51.85.
The main thing about Smith is that he has made alot of his runs against India and England who are top flight teams. Though he did also gorge on WI