The whole point of Equius and Nepeta's moirallegiance is that it is supposed to be the iconic example of a pairing functioning so well that everyone just looks at it and says "Oh, yeah, that's a moirallegiance there". They are the most successful pale red pairing in the comic.
When Nepeta starts to go off the handle, Equius calms her down and brings her back under control. When Equius starts to flip out, Nepeta cuddles with him in the horn pile and he remembers himself. The two of them are a carefully balanced pair, friends so close that they are there for each other no matter what.
Moirallegiance isn't just about calming down psycopaths, or else it wouldn't be something that every troll aspires to. It's about being a balancing force and support in someone else's life, and in return them being a balancing force and support in yours.
Equius and Nepeta are exceptional morails to one another. Karkat and Gamzee are very good moirails, and there's some evidence that Aradia and Sollux become decent moirails.
Feferi and Eridan were terrible moirails, because even though Eridan thought that he was helping and balancing Feferi, he wasn't doing very much of that, and she was wearing herself to the bone trying to rein him in.