I have a brand-new midmarket Kenmore gas range, which takes about 8-10 minutes to reach 350. I learned to my chagrin that the “preheat” buzz will ring after the oven’s only about 2/3 of the way there, which plays havoc with timing. I wait until my thermometer actually reads the temp I want.
BTW, I think what The Wiz was getting at in terms of steam and bread crusts is the steam generated internally as the dough heats up. A preheated oven will form a crust more rapidly, sealing in this internal steam. But my experience is that using a preheated oven will result in a lower rise, precisely because the crust forms more quickly - it gives less time for extra rising. That can be good for the bread’s texture, depending on what effect you’re going for - it makes the bread somewhat denser.
Now, as for heat loss when you open the door - assuming you just open it, pop your food in, and close it with no fussing around, you should’t lose more than about 25 degrees F. Even with fussing, I don’t think I’ve ever lost more than 50.