I think it's fair to say that Durant has the chance to be the best outside shooter ever among players 6'9" and over. Larry was a career 37.6% three point shooter, and had a career high of 42.7%. That makes him excellent, but not the best.
The game was a lot different then. In '86 and '87, Larry led the league in three pointers made, with 82 and 90, respectively. Those two seasons, *combined*, wouldn't put Larry in the top-80 all-time in most prolific seasons.
Players today grow up shooting the three, and offenses are designed to accentuate it. I think it's natural that today's players are going to be more familiar with it, and it's no surprise that today's three point shooters are sinking more shots, often at a higher percentage.
Of course, Durant is not the overall player that Larry was. However, I think it's fair to say that Durant, as a pure shooter, is in Bird's class.