I said seem. When the Cloud of Darkness talks to the Onion Knight he is just that, the Onion Knight. It's not you kids, it's a title referring to him specifically.
Warrior of Light is the same. He says he doesn't remember anything and then Tidus/Firion (don't remember which one it was, or both at different times) says that he'll always have the memories of fighting alongside the other Dissidia warriors. But like you said in another topoic, he remembers Garland from the events in Final Fantasy. If they actually acknowledged the fact that he had three others guys that also don't have memries and were with him from day 1 that would take away from that friendship moment with the Dissidia guys, so they skimped over that. I didn't say they retconned it outright, like you were quick to jump on but they ignored them in the coontext of this game.
Well for obvious plot reasons, they can't really say the names or anything of those characters, and for the reasons you said. And really, if the Onion Knights were to have a name, they'd be the names of the characters in the DS remake of FFIII, as shown in the Dissidia Ultimania.
Except that they don't work toward the same outcome. Emperor and Ultimecia do, Kefka, Kuja, Exdeath and CoD do. The rest they just cope with out of neccesity.
The outcome they *all* want, is a true death for Cosmos. After that, they know they're gonna do whatever they want. As Mateus states after Cosmos is killed:
Emperor Mateus near the end said:
With Chaos victorious, the chains binding us are no more. One schemes the world's return to the Void, while another revels in its ultimate destruction. Each of us has begun to follow the naked desires in our hearts.
It is the birth of an utterly chaotic world.
That about sums it up. And it makes total sense.
Ultimecia brought Garland to team up against Squall. Kefka brought CoD to team up against Terra.
Kefka wasn't interested in destroying Terra originally, he wanted to capture her and make her, his slave again. As for Ultimecia, that's a good point. She's the only real exception. She probably intended to beat the shit out of him, and push him to his limit, in hopes of making him squeeze out his crystal so their plot would work.
Also, I think its worth noting that in Shade Impulse, ExDeath, Emperor Mateus, and Garland, are the only villains that are by plot, faced off against, by more than one hero. These three apparently took more than one person to beat. Not just their respective heroes. All the others were defeated by their respective hero exclusively.