Dark backgrounds isn't necessarily"the key" ... it's more of a want or hope. I was adjusting an image last night from a redwood wedding. It was scheduled a specific time of day at a specific park. The entire park was scattered mix of sunlight and shadows. There was no "key" to find, nor time to go elsewhere. Sometimes it is possible to go elsewhere or another hour. Nice option if it's available. Partially cloudy days often cause changes that may make a dark background or light background trade places throughout the day.
Back the OP -- I think the main point was getting the people out of direct sun. Personally, the hot spots in the background don't bother me very much provided it's back in the bokeh. Some people may even prefer the bright spots of bokeh instead of an even darker background.
Good point. You can't always find dark backgrounds but even if you can't you can still get good pics by putting your subjects in the shade. Even if you don't have time to go elsewhere.