To be fair, Jorginho only came because of Sarri. If not for Sarri, Jorginho would have definitely been a City player where I believe he would have thrived under a system which is down pat. Kepa came because we had to get rid of Courtois, and from what I've heard Kovacic was thrown in by Real to sweeten the Courtois deal. There's no way we could rely on our current strikers to do anything, so Higuain was the only choice. The board had only backed Sarri with three players, two of which were desperately needed in a new keeper to replace Courtois and a striker.
I think a lot of the first season under Conte was a new system which hadn't been played against before, so that helped, but also the competition was limited. It was Pep's first season at City, Klopp wasn't doing good with Liverpool, and only Tottenham were playing consistently well that season. I agree with your points that Alonso and Moses played well that season, but again, think it was more to do with teams not adapting how to play against the system.
Luiz has always been a quality player with the ball at his feet. He was always world class on his day, so he certainly wasn't/isn't a poor player.
Nevertheless, Costa and Kante were arguably our best players in the first season. Without them, we had no chance of winning the league.
Sarri is in a league with more competition this season and I believe people need to curb their expectations a little. We were way off challenging for the title last season and starting off this season without a competent striker and trying to learn a new system set us back straight away. If we don't play as well but still keep picking up three points, then it's okay because it's all about believing in the process.