Net spend allows you to analyse how the club makes its money. Using it in an argument about how much Klopp does or doesn't spend is idiotic. Klopps comes from Liverpool's transfers, United's comes from them being a bigger club than you.
Your argument for Klopp can be used for Mourinho, as if he is just going to say "na Ed mate you have all that Pogba money the club has generated, spread it around the board, I'm happy with what I've got."
The fact is Klopp has had big money made available to him, the board did not need to reinvest player transfers into the squad but they did. And he's now gone out and spent it.
To say he hasn't spent anything is to ignore the basics of running a club. You made a profit, that profit was put into a "war chest" and Klopp went out and spent it. He is one of the biggest spending managers in the league, he's just been given the funds from player sales rather than merchandise.