How is he "a bad lion"? He doesn't even do the same thing Lion does. That's like saying he's a bad Kunkka because his ult is on such a long cooldown.
Stun that hits heroes in a line.
Ult that's a big nuke.
Mana removal.
Secondary disable.
They're pretty damn similar.
But Lion's secondary disable (hex versus carapace) is much stronger, and his nuke does a ton more damage (though at levels 6/11 has a much worse cooldown). For utility, Lion is much better.
Nyx's advantage I guess is that he can solo offlane thanks to his high regen... or at least he could, you don't really see him much these days so I'm not sure how successful he really is.