If you read the history of the depreciation of Mary it might give you pause for thought. Luther himself had a love for Mary, her role and called her 'Queen of Heaven'. He wrote a book on the Magnificat. So the European Reformation is not the source. It was Henry the 8th and Thomas Cromwell in England who bore a real hatred of any sort of elevation of her, but you have to wonder if their dreadful misogyny played a part in that. In retrospect, they didn't.
1. Luther really isn't on the Roman Catholic side. Saying Luther "loved" Mary lacks qualification. He certainly did not "love" Mary in the typical Roman Catholic 16th Century popular piety sense. In fact, he actively wrote against it. That Luther said nice things about Mary is not the same thing as Roman Catholic Marian devotion, both then and now.
2. Of the works of Luther that I've dealt with over the years, I rarely have come across Luther using the title "Queen of Heaven." The reason why is because "Queen of Heaven" was directly associated with the Salve Regina and the Regina Coeli. Both of these perpetuated the sort of medieval Mariolatry that Luther was against.
3. True, as pointed out, there is an explicit writing in which Luther refers to Mary as "Queen of Heaven".... his treatment of the Magnificat, but that's the only explicit positive reference to "Queen of Heaven" that I'm aware of from Luther. In context, Luther allows "Queen of Heaven" to be a "true enough name" but qualifies it that even if this name is applied, Mary is not "a goddess who could grant gifts or render aid, as some suppose when they pray and flee to her rather than to God. She gives nothing."
4. I anticipate this response from a defender of Rome: Yes, Mary is not a goddess. We agree with Luther. The Mary of Luther and the Mary of 16th Century Roman Catholicism though are different, for in that view, Mary is someone to pray to and flee to who grants gifts... hence, what Luther would call, a goddess. According to Luther, by pouring more into the term "Queen of Heaven" (like the defenders of Rome do), "we can easily take away too much from God’s grace, which is a perilous thing to do and not well pleasing to her." When Luther here says "Queen of Heaven" "is a true enough name," he does not mean the same thing Rome's defenders do. If there's any agreement here between the defenders of Rome and Luther, it's only surface level.
Luther's exposition of the Magnificat was seen in his day as an attack against popular Marian piety and is a transitional work in Luther's Mariology (not entirely reflective of his later thought). In chronological order, Luther's 1521 admitting a use of "Queen of Heaven" is followed by 1522's "doing Christ a disservice" if one uses the title. Then for the rest of Luther's career, the Salve Regina and the Regina Coeli were to be avoided as blasphemous.