After reading the most recent summer update, I suddenly realized that Stanley may not actually be attuned to the ArkenHammer.
Here's my basis for hypothosis:
Stanley, unlike Wanda, has no idea what he's doing with his Arkentool. He learned to turn walnuts to pidgeons after, what, years? Wanda was making decrypted warriors moments later.
The only real reasons people thought he was attuned was possession and the command of dwagons. Seeing that Ansom was in possession of Wanda's Arkentool, possession =/= attunement. Also, Parson commanded a dwagon pretty handily, though he is much larger than any Erfworlder, and can't really be expected to ride a dwagon successfully.