I believe, Luther himself shied away from the necessary conclusion that denial of free will leads to predestination of the reprobates as wll as the elect, and hence to God as author of evil as well as the good. Others did that step for Luther, most notably Calvin and Zwingli.
I don't think it bears more than a purely historical interest, who of the leaders of the reformed communities thought what. If you drop your computer from the window, it will stop working. What part of the computer broke in what order following the impact is a quandary for the curious mind, but that knowledge is not going to fix the computer.
Oh, I fully agree...the dropping of a computer analogy is perfect. That's why I "lump" Christians into two groups -- the Apostolic community and the other. Anything outside the Apostolic Churches pretty much satisfies "a quandary for the curious mind, but that knowledge is not going to fix" anything.
Our Churches have a providential chance of reuniting one day, but others, well that may require a miracle! :-)
Your quote from 2 Peter is the crucial element of truth about Bible-only based so-called churches. The Bible was not readily available for almost 2,000 years and the majority of the population could not read way into the 20th century, let alone understand the Bible in context in which it was written. Clearly, God'splan was was not every-man-is-his-own-pope idea and a proliferation of private interpretations.
The Fathers kept accurate records which show us how the Church phronema worked in context of the times when the Apostles still walked the earth. As Kolokotronis observed: chances are that they knew better than some Germans 1,500 years later.