For me, signing Sissoko was just plain stupidity. We had visibility to what he was because he was 26/27 at the time. Such a limited footballer who was never going to suit our system.
Very different for Sanchez who was only 20/21 and played at centre half. He wasn't a non ball player either at Ajax. In fact, he had no choice but to step straight into our first team with Vertonghen, in autumn 2017 because Toby got injured. He played 31 of the league games that season and nobody was complaining. Well Toby was, because he had to wait to get back into the team.
However, for whatever reason his touch and passing just couldn't be nurtured to the level we needed it. I would say his reading of the game and positional sense never plateau'd to where we needed it either. I can still see why our club saw some raw ingredients in a 19/20 year old playing for Ajax though. Centre halves grow immensely from 21 to 24 and you never really see their true potential until later. Davinson also did pretty well each time he got a run in the side. That never happened, and I think his head went eventually. He couldn't find consistency, just like before he left when he got boo'd one match and was MotM the very next.