As far as our draft history goes... pretty much every Celtic legend was drafted into this organization with a Top 10 pick. Pretty much every championship we've had was built on first bottoming out for an elite prospect or two.
Yes, people seem to forget that Garnett was an overall no 1 pick and Ray Allen was 5th overall (and took a 5th pick to acquire in a trade, a pick the Celtics earned by being bad). It's true that the linchpin of the Garnett deal was Jefferson, taken with the 15th pick. However, the age limit now forces high schoolers to spend a year in college which makes scouting them a lot easier.
Of course, this is all ignoring the fact that McHale did his old team a favor. He did not aggressively search for the best possible deal and he definitely purposefully avoided dealing him to the Lakers (though Gasol would later work out just fine for them).