A Protestant says:
This (Ignatius and mono-episcopacy) is one of the earliest and most discernible mistakes of the early church (post canon/post apostles) where they went beyond Scripture.
First reply: if St Ignatius (who lived most of his life in the first century, and was a disciple of St John) could get this wrong, there is absolutely no reason to suppose that the Protestants have got anything right in their distinctives, coming as they do some 1500 years and more later. St Ignatius had an apostle for his teacher. He didn’t have to resort to exegesis; he could simply ask questions.
Second reply: if the Church could go off the rails in the first century, there is absolutely no reason to suppose that the Protestants have put things back on them. The gentleman’s claim amounts to ecclesial deism.