Parson is the most dangerouse by a long shot (as he can break the rules and has non thinkomany (real personal) loyalty of the casters and Ansom). But Stanley does not know that. Stanely has always shown signs of paraoinia (after the battle at the donute he said something to the effect of I don't know if you failed me or betrayed me). Now that Stanley is NOT so special (there is another Arkentool wileder in GK) that is arguably more powerful (and face it a heck of a lot smarter and deviouse) he is scrambling to prove that he is top dog. In fact at some point in the future I really expect Stanely to try to do something to cut down Wanda's power and maybe even try to croak her.
True. Parson is far more dangerous, in the long run, than Wanda.
For the reasons you mentioned, and also because Wanda is now satisfied. She's gotten what she wanted. She achieved her goal. Now she can hang out and create uncroaked/decrypted all day, and occasionally indulge her interrogation hobby in the evenings. Parson, on the other hand, does not have what he wants yet... and achieving his goals will require that the world itself be broken and reformed into a new image.
Stanley, of course, seems unaware of all this... ...and I don't think he has the ability to think outside of the box enough to even perceive Wanda or Parson as a threat.
Stanley is, after all, their Overlord... using normal Erfworld thinking: how could units possibly be a threat to their own Overlord?
I don't think Stanley can even come to the conclusion that he should be worried about his underlings. More likely, he'll simply become irritated with them for some silly reason having to do with ego or pride... but I don't think he's capable of seeing them as a threat.