I have a personal theory (which I apply to myself therefore it is 100% correct.

), that says you cannot be both highly creative,
and have good technical skills at the same time. In other words, you can't design very creative graphics and also create the job in an accurate and technical minded way. I believe they are mutually exclusive. This is opposed to pre-press people, which need to be very technical but don't need to be very creative. That's the reason for the "clash" between the two, and I think you can read that between the lines in this thread.
Again, I had this theory from personal experience and the 10 years I've been working with graphic designers. Obviously I know there are exceptions, but as a general rule I think it's correct.
I agree wholeheartedly with you, that designers and printers must work together in a respectful manner - that's the basis of cooperation.
This thread will probably stay as a rant. I don't think any graphic designer will learn better technical skills from it (you might be the exception!). Many people don't like to change the way they work - "that's how we do things here" is a phrase I've heard too often.
Good luck to you!