Sancho had the ultimate power, actions speak louder than words, he made the decision to move away which was completely justified in my opinion, I would have done the same (if it wasn't City). However you can't look at that decision and say he faught for his first team place because he didn't, he left because he thought he had more opportunity to play elsewhere.
Even big name players have to fight for their place occasionally, even Aguero did when Jesus joined us. The easy option would have been to pack his bags and take his pick of any other club in the world, virtually guaranteed to be first choice wherever he decided to go. Aguero didn't, he had the character to stay and fight for his place, even as a world class establish player with legendary status almost guaranteed.