Well,if he will be good here 14 is nothing. If he is shit even 4 is too much.
This is a good point and applies to almost every player we sign.
Maybe exceptions are those veteran or veteran-ish players like Darmian. I wouldn't pay or have paid (even knowing how good he will be) 14m€ for Darmian. Maybe something like 8-10m€? So there is basically a room for players who are good for Inter but who Inter should not pay over 10m€. But yeah, pretty much exception cases.
So basically your assessment is correct, even though there are lot of levels between good and shit.
edit. But gotta add that's still pretty expensive given he's a player from Empoli who no one had heard of 6 months ago (because he had played like 70 minutes of senior level football in his career before 2022).