Your copper story is typical. The flux issue is a big one right now. The new codes are calling for water soluable fluxes. Many plumbers do not debur the cut ends of copper which will lead to erosion in the tubing near the fittings. I have seen this myself a number of times. But neither of these issues explain the pinholing you describe. FYI, I am an active member of the largest and most respected plumbing e-mail discussion group. There is a lot of fighting going on the last few days on this very issue of PEX vs. copper. We have the CDA on there as well as members of the PEX industry. They cannot explain the copper failures. Their excuses are weak.
Thanks for the info on the PB failures.
On the copper failures, I note that where I live, the available Type M is made in Mexico, whereas the Type L is made in the USofA. Could that be a factor?