To continue this discussion i did like you suggested with the “override in the simulation”.
I try to justify why people like “Loyal to the End” so mutch. (And find argument to convince my RL that Ancestral Resonance is better)
If i doing quick math i have:
Base Mastery 737
Ancestral Resonance 681 with 54.20% in average i have +369 Mastery
Ancestral Resonance stacked (3 times) with 54.20% (because it doesn’t change the chance of procs) in average i have +1107 Mastery
Loyal to the end provide +(178+6*44) (Be optimist on how many ppl have this trait) = +442 Mastery 100% of the time
Quick math : Ancestral Resonance is better
Here i have two simulation one considering the 644+642 bonus from “Loyal to the end”, the other being my default BiB
BiB - custom Azerith Rules - No Loyal buff
BiB - Default azerith rules - No Loyal buff
BiB - custom Azerith Rules - Loyal buffed
So to resume : even with 6 ally the “Loyal to the End” doesn’t seems better.
BUT Their is more differencies between the two gear.
so i tried this :
Comparing having two loyal to the End with allies buff
Default BiB
Here i gain 1k HPS and 1 ally death with Loyal To the End (WITH 6 allies having it)
But this rules benefits doesn’t seems to had up if i stack multiple of this trait.
(I had to change gear with higher iLvl one but doesn’t change for a better result)
Loyal to the End x2
It’s quite difficult to work with only one setup at a time 
I did one last thing: compare BiS with Loyal to the end.
Summary :
Loyal to the end with more than 5 ally is better compare to the default current gearing.
BiS - Loyal x3 - 6 Ally
BiS - Loyal x3 - 4 Ally
To summaryse This trait have a treshold and could be interesting to find the limit where it will take the lead and for wich class.
Putting a note in the guide for this specific one like “For Restoration Shaman; Loyal to the End is good after X people also having it”