TS- It didn't take Avery Bradley until his 4th season in the league to learn how to play. Do you not remember him taking Ray Allen's starting spot his second season in the NBA? And that was under Doc Rivers, a coach notorious for playing veteran guys over 1st and 2nd year players.
And it's kind of pointless to compare him and Austin in their 3rd yrs playing, when Bradley actually played better in his second season than he did in his third season-- most likely due to the offseason shoulder surgery he was recovering from in his 3rd yr, which you failed to even mention. --Clearly Bradley's efficiency dropped way off between his 2nd yr and 3rd yr. Not to mention the fact that Austin is only half way through his 3rd season, so its not much of a comparison to make at this point.
Bradley all day over Austin Rivers though...he developed a good shooting stroke quicker, and played solid defense from the get-go...which is something Austin has not shown he is capable of.