I perfectly understand your view, but let me explain a bit.
Scalvini is a solid defensive option and could be an asset for the years to come, so would be smart to take him and fix our defense as an european level, lets assume +30M for him, maybe loan at first year as often done in the past.
SMS is on his last year of contract with Lazio, so his price will be lower than the real market value, making the operation profitable even if we should resell him after a couple of seasons, lets say another 30M.
Hakimi will be feasable only with a Lukaku formula, loan with PSG contribution, looking what is happenening in their HQ recently can be a only a suggestion or maybe not.
Retegui is a real striker, more clinical than Lukaku and more physical than Lautaro, in my opinion a very good option to support our style of play assuming Inzaghi as our coach for the next 2/3 years, other 20M.
For 4 players we are going to spend a 80M budget, while getting rid of Correa, 20M or less, for Retegui with same value, and probably Dumfries, 35M, to make room for Hakimi, probably Brozovic, other 35M, in a swap with SMS at almost same price, to end mercato with minor operations with youngsters and reach the amount necessary for Scalvini.
I don't see impossible to take more functional players while improving our roster, depsite having to say goodbye to other players like Brozo or Denzel, this is how the whole system goes and player trading is a common way to improve competitivity while avoiding make more debts, Marotta showed us that even selling big names is still possible to reach UCL final and win domestic trophies, while when PSG and PL teams spending billions barely win anything, not to mention Barca and their debts.