We are talking here about how good/bad our record transfers have been.
And basically what you are saying is that "he makes mistakes and is kind of so-so player, but one day he might become good".
Thaaaat is awful recap for record transfer, sorry.
Record arrival should be someone who kicks down the door, is nailed down starter and leader at least in his line.
While in all honesty Sanchez has been just bit more than a squad player. 3 seasons after his arrival and in none of the seasons has anyone considered him "best defender of the season". So yea... as record transfer he has not fulfilled hopes.
I hope he can improve and iron out the mistakes, improve his focus and play calmer. But the fact is that he still needs to improve a great deal.