While I agree with you that McAdoo should probably have left after his freshman year, I don't entirely agree with your characterization of him vis-a-vis the other players you mention. Statistically, he had a much worse freshman season than Giles, and WAY, WAY worse than Bradley. The chart below shows some advanced stats for all three players during their freshman seasons:
Code:
Player PER TS% ORB% DRB% Usage% asst% stl% blk% Ortg
JM McAdoo 17.2 47.8 9.2 15.6 20.6 3.1 3.1 2.1 104.7
T Bradley 26.1 59.0 18.7 18.9 20.7 7.2 1.0 4.4 129.1
H Giles 19.8 57.7 16.4 21.5 17.9 5.6 1.7 5.3 115.1
Comparably, those numbers for McAdoo were
horrible. If he could have been drafted in the lottery, or even in the first round, then he should have jumped on it, because his deficiencies were obvious from his play. Giles numbers were much better (though not super-great) and considering his injuries an NBA team might reasonably project him to be significantly better than that.
Bradley's numbers, on the other hand, were outstanding. Maybe his smaller role made him look better than he was, though if so that's the opposite of McAdoo -- for an NBA team to have drafted JMM after his freshman year they would have had to gamble that the smaller role had
diminished his productivity and he'd massively improve with more reps. Unlike McAdoo, Bradley's freshman stats suggest he'd be a monster if given a bigger role. If he chooses to go pro now, good for him, but (again, unlike McAdoo) I don't see any statistical warning signs that suggest his stock would go down as a featured college player.