I'm struggling to understand why would you deduct the $600k.
Wouldn't it already have been "deducted" in the form of mortgage debt upon taking on the loan?
Think of it like buying a pair of Jordans and flipping it on StockX. You may have sold it for $1000, but that's not your net profit, you have to consider what you bought it for. The only way to compare a buyer to renter is to account for the fact that the buyer had to come up with over half a mil in the beginning.

bruh