In Sweden the pope urged atonement and Christian reconciliation. He also acknowledge that the Reformation helped give greater centrality to sacred Scripture in the church’s life, which is certainly true. It was the Reformation that led to the Church’s great Counter-Reformation through which God raised great doctors of the Church like St. Teresa of Avila and St. John of the Cross, who renewed the religious life of the Church with the reforming of convents and a strong catechesis. Ignatius of Loyola and the Jesuits spearheaded the CounterReformation.
The Reformation was what led the Church to convene the Council of Trent. So God brought good out of the bad. Luther had a right to complain about the corruption, though he didn’t have a right to invent doctrine and discard Church teachings, which brought so much division int the Church.
Also, a heretic is a Catholic that denies Catholic doctrine and is excommunicated by the Church. So one cannot call 21st century Lutherans heretics, as most are probably not converts to Lutheranism from Catholicism.