Nice tests and anylisis !
I didn’t never test it so far, but it was a fact for me since EA that the higher the thrall the better, still in same faction.
Then fighter i gived them mostly the best weapon i could, corresponding to what they used by default.
Archers, best bow to, and of course i love snake-arrows ! For my thralls and for myself.
Like you said, other arrows don’t work better than default ones, so i stuck with snake-arrows, simply the best !
Now what would be nice, similar tests for armors, and the upgrades for them.
Not realy sure how much upgrades are working for thralls, at least the last time they seem no more lose the upgrades i put on theyr armors like it happened a time. But there isn’t realy any reason they shouldn’t work on them after all.