This is too simplistic. The value of low-precision lies in a few different scenarios.
In the simplest case, you could use it to quickly bootstrap a model, before fine-tuning it at higher precision. That can shave off a lot from the overall training time. I don't know how much that would compromise the accuracy of the trained model, but it's worth considering.
Second, there are certain layers and weights where the impact of low-precision might be negligible, in which case there can be substitutions in the fully-trained model. I think convolution layers, especially those involving larger convolutions, are probably a good example of this.
Finally, the accuracy deficit of lower-precision weights can probably be compensated by increasing the number of weights, yet not to a degree that would cancel out the savings from using lower precision.
I'm sure the AI community takes a more nuanced view of reduced precision arithmetic. The hardware developers are just touting raw performance vs. accuracy, but that doesn't mean (competent) users are employing reduced-precision arithmetic in exactly they same way as higher-precision.