Sinestro gets Parallax, btw.
Pros for Thaal:
His yellow energy projects fear. That's how he beat Ion, slaughtered the skyfather plus Guardians, and even hurt the multiversal entity Volthoom.
Omni King can certainly erase him, but he's shown no resistance to tp/mental manipulation, and seems kind of simple minded. No reason to believe he won't be paralyzed with fear, to the point of catatonia.
And his durability is suspect.. Spike through the head while fear cowering could be enough.
If all else fails, he could always dump him in Quard. He'd be trapped there, away from the arena.