I'm not convinced that this is greater DR then a 5D3 could handle. It also lacks sharpness, contrast, and does show grain (noise).
Digital DR is better than is commonly assumed. E6 slide films ranged from 6-8 usable stops. C14 print films generally fell into the 10-14 stop range. B&W film had a wide variance depending on emulsion, developer, and development technique: 8-18 stops. Very few people actually pick their film, developer, and technique to get a really wide range out of B&W. And most B&W emulsions will have similar or less DR than a modern DSLR given standard development.
DSLRs are now in the 11-15 stop range when shooting RAW. Perhaps more importantly, there is unparalleled control over the color, contrast, and tonality of the final image, separate from the DR. With film if you wanted a wide DR you had to accept the other characteristics of the film. (Not completely true with film scanners since they open the image to digital processing.)
As to why you expose for highlights or shadows...
* An emulsion layer is a thin but three dimensional space of silver halide crystals of varying size, shape, orientation, and therefore sensitivity. As light strikes the emulsion the most sensitive crystals are altered first. A single crystal will either develop or not, there are no shades of gray at that level. As light continues to fall on the film, some of it strikes crystals which have already changed, adding to the time it takes to alter the least sensitive crystals. Film's sensitivity drops as it is exposed to light. In long exposures we easily observe this and call it reciprocity failure, but it's at play even in the shortest exposures. This is why film has more highlight than shadow range, and a softer roll off at the highlight end.
* Slide film is processed to provide a reversed image. In theory this should give the same DR but with more shadow range. In practice slide films always had less DR because they were engineered to have more contrast and saturation so they looked good when projected.
* Digital sensors build a charge as light strikes the sensor, and there's a hard limit on that charge. When they hit that wall there's no roll off, the photosite simply clips. They have more shadow range than film because they simply have less noise for a given sensitivity, so the soft roll off...and the room for error...occurs on the shadow side.