Absolutely not true. Exxonmobil employees absolutely know how to do the work that contractors are doing. The exxonmobil employee is giving out the work then spending the time spot checking, QC'ing the results, and aligning to the big picture. In order to do that, they absolutely need to know how to do the technical details.
If you've ever given a contractor work to roam free and report back, you will get garbage in return (hence our horrendous safety relief programs at just about every site).