Claudius I said north of 100m, folks said that wasn't enough. And now he's only worth 80m. People need to make their minds up.
Anyway like I said I don't really care about the math. This is a/the hypothetical scenario. Keep your superstar defender and you get to bring in either one superstar forward or one superstar midfield player or sell your superstar defender, and you bring in a superstar forward and a superstar midfielder.
And some folks think the first option is the way to go. I would go the other way in the blink of an eye. And Gabriel is one of my favorite players.