Having said all that PID controllers can be a pig to tune. Some people find fuzzy logic controllers are much easier to understand and to set up.
Having worked before retiring in a oil refinery I can agree that loop tuning a PID controller can sometimes be a challenge. It's not so much that it is difficult but rather it can be so time consuming that people lose patience.
One problem is that there can be such a process time delay, especially for temperature loops, that it takes some time to see if a specific tuning change made an improvement or made it worst. Some controller manufactures have added auto-loop tuning features into their PID controllers and a few I worked with worked pretty well.
Lefty