I do appreciate this type of analysis having a civil back and forth discourse with the mathematical rigor behind our staements being transparent. The philosophy behind assuming 50/50 between accuracy and kinetic/elemental is to create a build that is well rounded for any encounter you might face (some bosses have all/no tech and some bosses have all/no elemental). Obviously there is an optimum build for each boss if you take their accuracy into account, however, you cant really build to compensate for internal/elemental... except for having a HP/heals build over a mitigation build.... which is still a rich debate.
I think it is an interesting question, trying to optimize for any encounter you might face. That's actually precisely why I use the mean damage output of each type to compute weightings. Thus, I sum up all m/r+k/e damage, all f/t+k/e damage, etc. The resulting weightings produce a build which is overall optimal, but sub-optimal on a per-boss basis. Sub-optimally on a per-boss basis is unavoidable without regearing between each fight, so I'm not sure it's worth dwelling too much on this inevitability.
Most bosses do stay fairly close to the mean in terms of damage types. There are some outliers, like Soa and Kephess v2, but those are exceptions. So, it seems that optimizing for the mean is unlikely to yield results that are *too* far from optimal on a per-boss basis.
i still think that the 85% downtime of the healing relic, as well as the overheal, are somewhat good arguments against using it.
Downtime seems like a valid argument to me. It definitely results in a far spikier survivability profile.
However, overheal is a non-issue for the same reason that overheal on a self-heal can be discarded, at least as far as mitigation is concerned. The reason for this is that overheal on a self-heal is exactly the same as a healer overhealing on the tank. Think about it. If the tank has 2% less mitigation and proportionally more self-heal, there is no difference in the amount of output required from the healer for the tank to stay neutral. If the healer makes no changes, the self-heal will have 0% overheal. However, if the healer increases output to a higher level, they may not see overheal in their own logs, but the self-heal overheal will rise significantly. This is unnecessary healing, since the self-heal would have earned that HP back, given the chance. Thus, it is exactly the same as healer overheal and should be counted as such.
For this reason, I think we are justified in counting the self-heal towards survivability in the same fashion as mitigation, without deflating to adjust for potential overheal. This counts for the healing relic just as it counts for the conventional self-heal.