maybe Rich is setting him up as the real "Big Bad Guy" instead of Xykon
It certainly goes along with Start of Darkness.
He's the one who transformed Xykon into a lich (to make him immune to a magic-nullifying disease he was infected with), he even went out and recruited Xykon for "The Plan".
Basically, Xykon appears to be the real Big Bad Guy because he's Epic Level, and Redcloak is mid-to-high teens in level (17th now). However, if you'll notice, Redcloak is usually the one doing the actual planning and thinking, and letting Xykon think it was his ideas.
Redcloak is the brains of the outfit, the one who knows the real long-term plan, and the real leader. Xykon is the hideously powerful, but in many ways foolish, lich, that Redcloak recruited/created for The Plan. . .and is willing to indulge his many eccentricities and give him the illusion of being the real leader in exchange for his cooperation with executing the ritual on the Gate.
Xykon has far more raw firepower (epic spells and a noted fondness for Maximized Energy Drain and Meteor Swarm), he's a much bigger threat in a direct fight (demolished the entire Sapphire Guard in a few rounds), but in the long term Redcloak is the bigger threat.
For who's the real Big Bad Evil Guy? Look at it this way: If Xykon and Redcloak parted ways and Redcloak found a new partner and Xykon found a new minion. . .which pair would be the
real threat to the world? A lich and his lackey that wants to conquer the world and rule it as Emperor, or the high priest of an evil god with a master plan that could unleash a Lovecraftian abomination that can destroy all of reality and kill the gods themselves?