First off, a minor note - the more I think about it, the more I think that people are readying actions to hit spellcasters, because it'd be pretty bizarre if neither Xykon or V could cast defensively. And now, your feature presentation:
Ok, I'll say it once more, since nobody apparently noticed the first time:
There's no reason to assume that there was only one symbol on the ball.
Even if the Paladins have a 50% chance to save (and it's probably more like 20%), then having four symbols would drop that to ~7%. And note that Symbol of Insanity can be made permanent, so he could even have done this beforehand so as to not waste slots.
Secondly, the ball is just a flavor thing, really. He could just as easily have carried in a steel sheet with the symbols on it and flipped it around to face the Paladins. When someone wants to describe something in a cooler/funnier/more interesting way - which is mechanically the same - then I (and all the DMs I know) would allow it in a game, much less in a comic.
Third, there's a lot of stuff that happens "between panels". Here's a probable reason why the front line of Paladins stopped attacking him:
Panel 6: Paladins finish their turn of beating up Xykon. Xykon points behind them (free action).
Panel 7-8: Paladins look around and realize it's going to be a bad day. (still the same round).
Panel 8.5: Xykon casts Horrid Wilting and kills all the Paladins next to him except the blue-beared one. (standard action, he's still got a move action

). Then the blue bearded one decides that it's more valuable to stop the slaughter/protect the throne than attack Xykon by himself.
Panel 9: We see the blue-bearded one doing exactly that.
Fourth, the Paralyzing Touch. Yes, this is quite risky, probably. There's a few options:
1) Xykon was careless but got lucky (certainly possible).
2) Xykon already cast Wall of Force in front of the gate, as backup.
3) Xykon has for some reason, researched a high-level paralyzation spell which happens to be called Paralyzing Touch. Unlikely, but hey, he did research Xykon's Moderately Escapable Forcecage.
Fifth, I think this served an important story purpose. It sacrifices somewhat the eliteness of the Sapphire Order, but that's in order to show that there's a reason Xykon is the BBEG - that he does more than pretend to fall asleep during planning sessions. Redcloak has been doing most of the work recently - it's time for Xykon to go back into action, less he become a farce.
Finally, a note on "realism": I've played a high-level spellcaster. As a 17th level human, forget 20th+ level Lich, he could have pretty much ended this battle in one round.
Step 1: Time Stop.
Step 2: The Paladins inexplicably find themselves underwater, taking acid
and boiling damage, being grappled by tentacles, in the dark, and trapped in there by walls of force (good luck dispelling those without being able to breath or concentrate).
Step 3: Profit!
And it doesn't mean that the Sapphire Order was puny either - it just means that a big enough level disparity is like using slingshots against a tank.