That's an interesting point, however I believe a distinction must be noted. God promised His Church would never fall into error, however He never promised its members wouldn't fall into error. Indeed, the Church is comprised of people, who are sinners. The historical events you cited didn't change the Church, in a doctrinal way. t led to many falling away from the Church, but ultimately that was the result of human error, not the Church Herself failing.
"t led" should be "They led..."