If you are claiming that Fernando has been a successful signing then you really are clutching at straws. The others have all come for huge fees and have yet to really justify them - although KDB is obviously class.
The list would be at least twice as long for all the players who have flopped, most notably the centre halves.
Txicki may well be doing a great job with the rest of the club, academy etc. I wouldnt know as I am not sure exaclty what his duty's are and what he does on a day to day basis. But most of his transfer dealings have been really poor.
Maybe we need some better scouts to help him out? Southampton seem to have a massive player turnover each season, yet they manage to find good replacements. Their academy aint bad either!
Fernando has been a successful signing. He cost £8m and is a perfectly good squad player who has some brilliant games in the right circumstances - when we're aggressively pressing and counter attacking.
A squad player, doesn't mind spending large periods on the bench and who comes in and does the dirty work when Fernandinho isn't around. He'll come in to the side and add some physicality to help out. He even did a good job at RB when asked to help out against a big WBA side.
Every good team has players like that, Fernando is ours and he's fine.