Guys there are many reasons why Pinamonti is worth less than those 2 sassuolo strikers and all are valid ones:
1) Both Raspadori and Scammaca have played for Italian NT and are considered part of the 1st team by now. This enough is worth 5-10 M more in the market
2) They have a perceived talent ceiling which is higher than the one expected by Pina. Even though , as of today , they might have the same stats the expectation cross scouts/directors/medias etc is that their potential is higher than the potential that Pina has . This also is worth 5-10M at least
3) Pinas wage is too high for his current ability . This decreases the negotiation power from the club because whichever team decides to buy him has to spend more on his salary therefore they try to reduce the spend on acquisition
4) Pina is a player completely out of the rotation at Inter , everyone knows he won't play a minute if he stays and everyone knows Inter needs the money. Raspadori and Scammaca on the other side were/are key players for Sassuolo , a club which doesn't need desperately to sell and has proven in the past ( Berardi ) that unless receives an offer considered enough won't sell . All of these influence the negotiation price of the players
If the above reasons weren't enough just ask yourself a question. If you had Lukaku , Lautaro & one of Correira/Dzeko in our roster and without even spending any money you had the chance to pick one of the trio Pina/Rasp/Scammaca to be our 4th striker , which one would you pick ? I am sure Pinamonti would always be the 3rd choice behind the other two...