What I'd suggest wouldn't be something that I'd do lightly, easily, or without actual feelings of heartbreak for all involved. I'm not one of those who is an arm-chair gloater over the misfortunes (or punishments) of those who 'could be' at the receiving end of God's disciplinary measures.
What I'm suggesting about the Old Covenant is that the Blessings and the Curses of the Law were no passing matter; that God wasn't actually joking about it when He established the Old Law for the Hebrews/Israelites/Jews. And without getting to much into the details, I will side with Jesus and His Apostles in how all of the prophetic structures within the Old Covenant would play out for those who refuse the Renewed/New Covenant that is found in Jesus the Messiah. That is to say, in heart-breaking terms------terms which again I don't say lightly or with any ounce of glee as some racists or anti-semitic folks might say it------the Jewish people, if not reconciled to Jesus, leave themselves and have left themselves historically vulnerable to the exact same kinds of discipline today that their ancestors experienced more than once during Old Testament times, up and through the era of the 2nd Temple, and then all the way to today as a part of the 2,000 years since those times.
As for the specificity of the Holocaust, we might also remember that many people of other nations also felt the murderous onslaught of Hitler's forces, with the Russian people taking the lion's share of deaths/casualites in World War II [about
20 million or so?].
World War II casualties of the Soviet Union - Wikipedia
So, in just looking at both World Wars 1 and 2 combined, we can all together wonder in awe: "Where was God in all of this?"