Before I took a deep dive on Hampton, I had him somewhere around ~20. His stats in Australia are really scary, including the numbers you pointed out.
The Spurs are known to be one of the better teams at developing players and if you're looking for a raw prospect to develop, Hampton is pretty high on that list. Extremely fast, great burst, good size at 6-foot-5, good touch, etc. And then when you factor in that he was basically a junior in high school who reclassified to a senior and then went pro all within a couple months -- his struggles in Australia are pretty understandable. Australia isn't a great league but they have a lot of former, old, desperate NBA-ish guys at the guard positions who didn't hesitate to beat him up.
Plus, Hampton only played like 300 minutes in Australia. I don't think it's wise to make any decisions based on a sample size that small. For example, Keldon Johnson played more minutes as a rookie and if we go by his numbers, we'd be counting on him to be a better version of Kawhi and we'd be celebrating his 100th percentile three-point jumper.