I think net spend is pretty irrelevant to be honest. (Except when it comes to the books).
For years, if we sold a player, we wouldnt have seen all of it reinvested as a general rule of thumb.
If we sold Niasse and Cleverley for £20m and bought Klaassen for £20m our net spend may be zero but our team has improved dramatically.
And that's all that is important. "Are we stronger now than before the window". As long as money is released to allow that to happen then we are doing the right thing.
(And that isn;t even taking into account that someone paying £50m for John Stones comes nowhere near to equating to £50m in our bank account. For fuck sake, the £90m for Pogba takes into account £41m going to his agent)