You aren't missing anything, I made this point in his hiring thread that apparently many ppl don't want to hear. Parker, while possibly an improvement over their previous coach (wont be saying much) is overall a negative for the program, and definitely not some difference maker.
His "proven record" at WW is that of chronic under-achievement relative to the level of talent there. Hell, they missed the playoffs with the RB who is going to be OSUs starter as a true soph this year. WW had incredible advantage in being able to collect the best players out of several different districts, had several high level D1 college players, and yet never accomplished anything that a team with those kind of athletes should have.
The hallmark of good coaching is winning games that you shouldn't on paper. WW never did that, and quite often was in extreme danger of losing games that they definitely shouldn't lose, due to the execution, discipline, and play calling issues you mentioned above.
Princeton has a very good class of kids right now, and will probably go a long way based on their talent alone. Kind of like when Brady Hoke inherited a good group at Michigan and won 11 games his first year. But after a couple years, the coaching comes thru and they were 6-6. Expect the same type of deal here at Princeton.