I won't make a case for Matt Bohannon to be the best all round SG in the league, because he isn't. He is, however, likely the best pure shooter.
In conference play Matt Bohannon had a true shooting % of 63.8 (Beane was next at 59.3), was 2nd in effective FG percent at 63.1 (none of the others mentioned in top 10), had the most threes made (by double digits), was 2nd in 3pt % (45% and 46 for the season) He had a rough start to the season, and at one point was at something like 12% from 3 about 8 games into the season. That tells you how how he got, and stayed, the rest of the season.