Every club has bad buys. He was as involved in the process of signing the likes of Mangala and Bony as the managers, performance analysts and scouts. There is the infamous story of Txiki pushing for Dybala but Pellegrini forcing Bony though instead as an example.
Cook had carte blanche to go and throw 250k a week at Yaya at a time when wages were not at that level. The project was in its infancy also but we cant really believe that Yaya only came for that, he was probably given 5x his wages to move here. Silva and Aguero the same. Cook went after big names and needed to make an impact, he signed Adebayor, Tevez, Aguero, Nasri and many more.
The likes of Marwood also massively pushed for Rodwell and Sinclair etc by all accounts because he had some sort of affinity to signing english talent I guess and look how that turned out.
Txiki is by far and away the best DoF on the planet, its pretty easy to see the huge success of CFG on the pitch and off it.