According to Evangelicals, before the Reformation, who were Christians if “Catholics are not Christians”?

Every now and then I hear non-Catholic Christians, usually Evangelicals, say things along the lines of “Catholics are not Christians” or “the Catholic Church does not teach the true Gospel.” Unless I am mistaken, Catholicism and various Orthodox Churches were virtually the only Christian “denominations” that existed before the Protestant Reformation, aside from a heretical sect here and there (e.g., the Cathars). So for those who think the Catholic Church has abandoned the true faith or Gospel, do they identify anyone from the time period of the fourth century A.D. until the Protestant Reformation who had retained the true Gospel?