Kawhi was a bit of a late bloomer when it comes to cultivating his skill set, but at this point he's legit and it's more mental now; i.e. imposing his will in tightly contested playoff games vs the Clippers, Thunder, Warriors, etc.
As far as the skillset, some players grow up with NBA player dads who can indoctrinate them into certain habits at a young age, others have a great AAU system or go to a great college program. I don't follow college bball so i've only heard that Kawhi was pretty much like a pf in school, so i dunno whether they saw his height, wingspan, hands,etc and kinda just typecast him as a shawn marion at best (with no emphasis on offense) or just where the disconnect came from... b/c he sure as hell seems to have the work ethic... and the Spurs definitely picked up on it