But here's the thing - moiraillegiance goes both ways. Moirails (note the spelling, please) take care of EACH OTHER. It's not just one way. Eridan was a whiny jerk, and Feferi was a naive kid, but she tried to help Eridan and he didn't try to help her. Also worth noting is the relative prevalence of genocide complexes in Alternian society. Eridan's ideals wouldn't be that uncommon, and not very worthy of note. It would be more like having to look after a loud dog, who you were supposed to be playing with. It was just loud, all bark and no bite, until it unexpectedly killed you after you went to your friend's house.
Also... Kanaya<>Equius (note the spelling again, please)?? What? Where did Kanaya come from? Did you mean Feferi? Plus, Equius is already Nepeta's moirail.