There's engineers, and there's engineers. The structural guys and gals make the buildings stand up and stay there. The rest of us make the buildings work. If a building were an animal, the architect's domain is the body plan and its exterior appearance. Structural is obviously the skeleton. Electrical is brain and nerves (especially since the profession now includes data and telecomm), HVAC ("mechanical", in the parlance) is the lungs and heart. I, among others, handle the circulatory system and the bowels.

I had a brief professional brush with an aspiring "designer architect" (as Steve calls them down below) a few years back, in that my employers at the time were engaged as his engineering consultants. After one of his proposals (for which we provided basic information about its interior workings) failed a design competition, he succeeded with the next one. Unfortunately. Because we then had to make it work.

Example lesson: Curved corridors are a major pain in the ass. The sheetrockers have no better time than we do: stud frame panels come in straight lines only. So does pipe. So, as it happens, do budgets.

"Mere contractors" sometime seem to build things in spite of architects. Sometimes that's necessary. Fortunately, that sort is a tiny minority in a profession of creative competence.