And yet to me somehow Yakuu feels much less volatile and subsequently safer to be around than at least the following three.
I thought the same so I did some counting. The numbers don't seem to add up for Kendra at least, she's got
-2 kills in the intro sequence (house crush & sister sandwich)
-2 kills in the cave
-1 kill if he keeps his distance after she leashed him
-1 kill when she pins him to the wall with her butt
-2 kills during the threesome with Trish
-1 kill if told that she should let Vai'klis die
-1 kill if spooked while hunting ghosts
-1 kill if you insist that Vai'klis feels cold
for a total of 11 kills, 10 if you consider the kills in the cave the same but I digress.
I didn't count Nyxmay's kills when the game kept going on, only deaths followed by "game over" screen. Also I wonder why you feel safer around Yakuu than Kendra. Kendra lets slide much more of your f*ckups than Yakuu, even insulting Vai'Klis, thus having twice as less death endings.
She kills you on two separate occasions for insulting Vai'klis, I wouldn't call that merciful