Being a simplex priest had nothing to do with how often they would serve (like a hermit) but rather with adequacy of their training/education. In the old days, faculties were not necessarily automatic with ordination and were granted separately in addition to ordination. St. John Vianney wasn’t given faculties to hear confession until months after ordination. Fr. Solanus Casey is the only person I heard of that never received faculties to preach or hear confessions. After Vatican II, the practice of having simplex priests was discontinued.