This would imply a failure on God's part, then.
Well these ideas, as I said, are a bit sketchy.
Fall of the Angels, and why permit it?
Perhaps G-d made the angels only to choose between various good options (the nature of G-d's free-will), but because of the way He made reality, it was possible that the angels might get tempted to do evil. Such possibility of temptation would not be part of G-d's intentional design, but an undesired, yet anticipated, side-effect of His design.
Now G-d had the choice of protecting His angels outright from receiving such temptations, from the very start. But He didn't do so (maybe), because even though the temptations weren't intended, they did facilitate that great good of angels rejecting evil and choosing good. Without such temptations, they were only able to choose from several good options, which isn't as good, as the triumph of good over evil is.
In such a scenario, G-d didn't will evil, but merely anticipated the possibility of it, as a side effect of how He had designed reality, and chose to tolerate it, because it enabled the great good of His creatures triumphing over evil, with good, through the exercise of their free-will.
After the 'Fall of the Angels', G-d decided it would be better, if He rewarded the good angels with permanently removing all temptations from them, such that they could only choose good. Even though the 'triumph over evil through free-will' was better than simply choosing good from only good options, in a normative way, there was a goodness in 'crystallising' the good angels' goodness by making them permanently good, that inclined towards doing such 'crystallisation'. Also, if G-d allowed the testing period to go on further, more angels may have fallen, such that there would come to be a 'tipping point in the balance' inclining towards doing such 'crystallisation' sooner rather than later: you don't want all the created angels to fall.
So these are some thoughts to answer your comment. They are sketchy and not solidified, but I felt that perhaps this would help you and others.