> back tested it shows significantly lower variance
Not sure what you're using as the measure of variance, but Morningstar found DCA has higher variance in IRR: https://www.morningstar.com.au/learn/article/the-dollar-cost...
> These are not mutually exclusive. One can lump sum all into the lowest risk allocation and then risk on over time
I never said they were mutually exclusive, just that it is suboptimal.
> In every other scenario, the DCA is strictly worse.
Yes. And so what? It will always be the case that a lower variance approach will be better in the cases where the higher variance approach did poorly and worse otherwise.
> it's better to choose a less volatile asset allocation
These are not mutually exclusive. One can lump sum all into the lowest risk allocation and then risk on over time.
It doesn't help that right now there is not much freedom in asset allocation at all. Your choices are pretty limited to higher risk things and things with a negative real yield.