But rent is not subtracted from the total profit at the end while the mortgage is.
If we assume they rent a 400k house, let's be generous and assume they get it at 3k per month, and that rent doubles over the thirty years. The total rent would be 1.5·3000·30·12 = 1.62 million dollars. This eats quite a bit into the 1.8 million dollar profit.
Monthly rent and mortgage have to be similar for the argument to work. You would obviously not be renting a $400k house in this scenario, you would be renting a $1562 per month house.
But rent is not subtracted from the total profit at the end while the mortgage is.
If we assume they rent a 400k house, let's be generous and assume they get it at 3k per month, and that rent doubles over the thirty years. The total rent would be 1.5·3000·30·12 = 1.62 million dollars. This eats quite a bit into the 1.8 million dollar profit.
Monthly rent and mortgage have to be similar for the argument to work. You would obviously not be renting a $400k house in this scenario, you would be renting a $1562 per month house.