Hi Greg, you are right, in Wales the name was not commonly derived from Joan, tho' this is sometimes the case in England, also Jene, Gene, Jone, Johan or John.
To quote from the P.H. Reaney dictionary of british surnames, "The Welsh form was Ieuan,Evan(v.Jevons, Evans).The form Ioan was adopted for the Welsh Authorised Version of the Bible, hence the frequency of the Welsh patronymic Jones."
Incidentaly Stephens derives from the Greek word for "crown" a name found in Old English but only as a monk's name.It became common after the Conquest.
cheers
bill