If we were acquiring Chiellini today or another player of proven value, he wouldnt cost only 4.3 That means that his estimated value is no longer 4.3, but more likely near the sum you mentioned. But if we were singing today a 35mil CB, then yes the expectations of him would be big enough to demand a better performance due to the much higher expectations!
If that player failed to perform better than Chiellini or worse an even less valuable player, but still had a decent contribution as a sub,
even then his transfer would be considered a failed one.
There are many reasons that affect the value a player at any given moment, his age, potential, fitness, form , health, remainder of years in his contract.
If we consider all these, then we can draw some safer conclusions,
but there is no doubt that the the transfer fee represents smth of the current value of a certain player and def affects our expectations and their duty/responsibility to the team!
For ex, if we sell all of our RBs now and sign a 15mil RB and a 1.5 mil RB, of similar age, contract and fitness levels, but with a far different potential and average performance.
The 15mil RB, not only ought to be our first choice players, offering far better than the 1.5 nil sub, but also prove his worthy against similar valued opposition players!
Whilst on the other hand, we must only expect from the 1.5mil player to perform decent enough against similar valued opposition and he shouldnt be blamed for not being able to cope with the 15mil attacking wingers, as the 15mil would...
IMO he is not a flop if he can do his job against the similar valued player, but failed to compete with the best.
On the other hand, i expect more from a valuable player and i do consider him a flop if he fails to perform against players of similar value and only provides better performances against the lesser opposition!
If the player fails to offer average performances according to his value (that includes; potential, talent, fitness etc) then it is his fault, or the coaches fault, who failed to make the optimal use of his potential.
But if he does his job, though this wouldnt be enough to save the team's performances, because the performances needed, extend his maximum potential.
Then the fault lies solely to the managers for making a faulty estimation and decision, to invest on him, rather than choosing the right tool for the job. (like it is the case with Molinaro)
With Tiago, it is mostly the first case, but with Poulsen for ex, it is the second case...