I have issues with your analysis already xD
You basically make strong independence assumptions which probably don't hold.
You discount the slashing debuff utility of these jobs on the premise of "it's likely that the dps bring these if the tanks don't".
But these are not independent- it's because the strongest dps combination always has a slashing debuffer that you can afford to go PLD/DRK.
This is already an issue itself, but I'm not comfortable just discarding this piece of utility because we implicitly assume that "it's always there" (which shouldn't be the case, but that's how centralising NIN really is these days).
Also 5% is a lot. If you raid, you've seen many low% enrages. Now think about that one week where you were stuck on A8S at sub 10% and consider that half of those would've been clears if you were using the meta comp.
You can't tell me to disregard this (and, seeing the slashing debuff comment, this is a slight underestimate under your questionable premise xD).
Another issue I have is that the multiplicative argument goes both ways- if you have a very strong base dps, you get more out of some buffs. Dragon Sight, Ifrit's single target thing (Devotion? Something like that qq), single target balances (sometimes you just get these and you need to dump them on someone) all work much better on a SAM. In some circumstances, it may be that the aoe multiplicative effect of buffs favour a all-around utility comp, but in some others (especially with those I've named), they flavor having a powerful single target dpser.
If you want a statistical look at it, there's a very strong correlation between NIN+SAM cores and very fast clears according to FFlogs, going by the top 20/50/100.
Does this imply causation or is it an anomaly?
Imho, it's a case of causation (that core works better because it's inherently stronger).
Caster-statistician rant out.
(That said, I really appreciate the effort and the fact you neatly compiled this wealth of good information is very much appreciation. Keep it up, friend)