I don't disagree with anything you said. If we hired Kevin O'Sullivan this summer and the dude went back-to-back seasons without making the tournament, people would be losing their shit.
The last part of your post rings very true. It's college baseball. The best of the best are still going pro out of high school. Bullpens are an adventure, fielding is an adventure, light posts in stadiums are an adventure.
At the end of the day it's a results business and the results have ranged from decently good to very good for 90% of Pierce's tenure. That said, I agree that the results have been much better than the process. And the process is likely not sustainable at its current rate. Weirdly, the biggest mistake of his tenure was bringing in Woody Williams. Not because he wasn't a good pitching coach but because the guy had never recruited a day in his life and based on what I understand he was getting murdered on the recruiting trail. It was a huge self-sack by Pierce to not recognize the issue before he hired him or structure the staff in a way where he didn't have to go out on the road. As a result, he had to fire his second pitching coach in two years and at that point, you aren't attracting any candidate worth a damn, there is no stability and player development/acquisition suffers.