Keep in mind that the comment to which you were responding was made almost 8 years ago. There have been significant changes in digital console hardware and use over that period.As a high school student, I would have to argue that comment. My church uses one of the more advanced digital sound boards out there(not sure which make/model as I don't operate that particular board). And most of the operators of that board are high school students. And they mix extremely well. It all depends on your training. On are equipment we shadow for a couple weeks, then we let them operate under supervision for a while, and THEN we let them run a service.
You do make a good point that training can be critical but the unfortunate fact is that many schools do not have the people or resources to properly train others on aspects such mixing and as digital mixers. In fact your comments reflect my experience that many students learn about mixers, mixing and audio primarily via involvement at a church with greater technical staff resources and then transfer that knowledge into their work at school.