Is a great athlete by most measures? Sure. Is he considered one when compared with the rest of the NBA? Nope. Quick but not elite, slight of frame and lacking great strength, not an explosive leaper and simply not a guy that jumps off of film as a specimen. There are plenty of NBA players with good to great careers who could be viewed similarly. All professional sports are preoccupied with the athletic marvel who drips with potential. Every year when guys skyrocket up NFL draft boards based on 40 times and measurable instead of game film I just shake my head.
But I digress.
Lin is making the most of an opportunity. But as someone who watched him and liked his game in the summer league I didn't think he was capable of this and neither did anyone in the NBA or he wouldn't have had to showcase himself just to make the deep bench of NBA rosters over the last two years. He's definitely a guy better suited for the NBA than the college or high school game (given the greater spacing in the pros) but even then, he's simply been a surprise.
Otherwise we could ask if Steve Nash would have been a higher pick and an all-star earlier if someone had seen his potential and he'd gone to a basketball powerhouse rather than Santa Clara. And some guys are just late bloomers (Scottie Pippen) and some simply have a rough road without breaks before they finally get their opportunities (Raja Bell among many others)
Scouts and evaluators miss on players all the time because they don't jump off the screen with amazing ability. It's why Tom Brady was a sixth round pick and why Billy Bean was able to assemble competitive A's teams on the cheap.
Perhaps I'm naive but I simply don't see any evidence of Lin being overlooked due to being an Asian American. In my junior year my high school team won the northern California championship for Division II though we lost in the state championship. I was the first guard off the bench behind two asian guards, both of whom got plenty of attention from college scouts, with our starting PG getting a full scholarship.