The idea of starting with and arbitrarily limiting yourself to a 50mm goes back to the days when zooms were generally poor quality and we were shooting Kodachrome, Ektachrome and Fujichrome an color films at what seem to very low ISOs, in today's lens.
On a full-frame camera a 24-105mm is a much better all around lens. On a crop-sensor, a 35mm lens gives closer to the perspective of what used to be called a "normal" lens that presented something relatively close to our eye's perspective.
This video sells way to short the ability for most modern cameras to shoot at high ISO and get clean results. I run into people in the field regularly, shooting too slow for wildlife or sports. When I ask what their ISO is, it's something crazy-low, like ISO 250. Get the shutter speed up and raise the ISO accordingly. Cameras as old as the original 7D could shoot at ISO 1600 and clean up nicely. The latest bodies are stunning in that regard.
What's in my full-frame bag? 12-24/f4, 24-70/f2.8, 100-400/f4.5-5.6, 500/f4 and 1.4x and 2.0x teleconverters. If portraiture were a big part of my life, I'd consider a bokeh-queen, like a fast 85mm, but that not a significant part of my work. There's no good reason for a 50mm.
