Did I miss something? The Sarrukh are potent adversaries, but they don't look anywhere near a CR 21 creature.
HP: 133
AC: 30
Attack: +23
F/R/W: 9/11/13
SR 20
Fear (DC 21)
Poison (DC 22)
A few Spell-like abilities, none over 4th level except teleport and wall of force (which are only 1/day.)...