This is the very root of this question. To me (and probably most of the other “no” voters), to be under a “spell” connotes a removal of free will. Think of Prince Eric choosing to marry the evil sea witch Ursula while under her spell (I have young daughters, ok?). That is an unacceptable proposition because, as others have noted: 1) it removes our culpability for everything we do, 2) it removes or negates a God-given gift or faculty both of which 3) make Satan (at least seem) more powerful than God, which is logically impossible.
Now, I 100% agree that the Enemy’s influence in this world is very great. But he has no power apart from God (in fact, Satan, as a creature, would not exist if God didn’t will it through His creative action) and works through whispers in our minds.
As to the question of the relative proportion of saved souls, we cannot know this and are commanded not to judge others’ salvation status. Who knows what will happen at our particular judgments or at the end of time? Perhaps God, in His mercy, will give us a peek at our lives as He saw them and a final opportunity to embrace Him. The way may be narrow, but as anyone who drives in Southern California knows, that doesn’t mean it can’t accommodate an infinite line of people. We just may need to spend a very long time in Purgatory to get there.