The Imp Sacred Defensive stance bonuses (+PRR/saves/threat) work fine without shields; the Gtr Sacred Defensive stance bonuses don't (CON/STR/HPs), same as Stalwart Defender. For 12 APs you can pick up +25 PRR, +3 to saves, Div Righteousness, +50% threat amp, and 3 extra LoHs.
Other than that, I agree with you.
In what way? It only procs on vorpal strikes, which last time I checked is 5% of all atks. Are you able to make 20 atks in 3 secs? Plus it has to be born in mind what you're giving up by taking T5 KotC; that means no Keen Edge, no Staff or Knife Spec, etc. It seems a reasonable tradeoff.