That’s a terrific question and one I’ve been thinking a great deal about. First of it the link above links to a preprint dated 2020. Has the paper not been published by 2021?
For a long time I did not like residual mean life as a solution to non-proportional hazards. I’m changing a bit but would you mind moving your post to https://discourse.datamethods.org/t/restricted-mean-survival-time-and-comparing-treatments-under-non-proportional-hazards where I’ll respond? And please add something to it when you move it related to the preprint status if you can find that out. Thanks.