Milito wanted to return to Genoa when Zaragoza was relegated even though he had interests from Valencia and Spurs. Motta was so often injured that he signed only a 1yr deal with Atletico. Dante was never a top quality player.
Quaresma is an example of Mou wanting a player which history predicted was more likely to fail than succeed at Inter. Yet he got him at a steep price.
The problem is that Perisic is still playing at an average club at 28, so why do you compare him to players that have moved to a top club at a younger age? He is at an average club and he is not setting the world on fire.
It matters if Perisic is worth the money or not, otherwise we can pay 100m to buy every average player that is good enough to play for United. If was coming for less or even free then there is less of an issue.
It is even worse if you dont care about money, because shouldnt we then get the better players if money is not a concern e.g. we can just buyout Carrasco for 100m. Carrasco is 23 and already a better player than Perisic.
We are only getting 4-6 players in a transfer window, and we have to make them count so that we can be competitive next season. The team lacks quality players but have abundance of average ones, so we cannot afford to add more mediocre players before addressing the lack of quality. Players like Perisic are what you add to fill in the holes of a team with an established core.