I think we are in dangerous waters when we are are basing public policy on "ability" to have impact opposed to "actual impact. I think it is a genuinely interesting question if and how much this variability contributes to the grid capacity requirements.
You can basically think of individual variability as noise on an analog signal. Does single user variability average out, and if so, on what scale?
How does this variability compare to other amplitude changes, like aggregate or seasonal daily use patterns?
I think it is entirely possible that this noise could be negligible at most scales, but obviously dont have the data.
However, someone with the actual data could easily do an ANOVA evaluation, and see what the actual numbers are.