No, there is another variable you are leaving out: justice. If the one suffering person voluntarily endures terrible suffering so that everyone else can be happy, that is a just world, and that one person is a hero and a saint. That’s basically what happens in the story of Jesus dying for our sins. But if that one person is compelled to suffer against their will, that is unfair and unjust, no matter how happy it makes everyone else. Fairness and justice just don’t figure into any kind of utilitarian calculations, and that is why utilitarianism can’t account for all of our ethical intuitions. You can simply turn off that intuition if you want to win this argument enough. some people are willing to do that, and some people aren’t. That’s why utilitarianism hasn’t won this battle, and probably never will in my opinion. But there are a lot of people who agree with you and disagree with me. That’s the way philosophy always works.

Your point about using percentages instead of absolute quantities is a good answer to that particular objection. I actually thought up that argument myself, and I’ll probably retire it now. But the other arguments have been around for centuries, and the question remains unresolved.