You are right the emphasis is really right now because the team and fans don't seem to have the patience to wait as they need results as soon as possible even if the consistency is not 100% but at least they should be positive signs that the team is heading somewhere. Chelsea was impatient too and Maresca changed things for them instantly that's the same thing United fans wants but sincerely Amorim's stats is really bad.
You just read my mind, I said the same thing about Manchester United defense but some people argued that the defense is okay, I really don't rate any of their defenders at all they really need to change the entire defense or at least get new players on each defensive position as you mentioned and also to be competitive they need a good defensive midfielder because I don't really approve of Casemeiro anymore, he can't give 100% with his age. They need to really sign more players to be honest. The signing of Cunha, Mbuemo and Sesko is good but more work needs to be done.
Casemiro is still a very solid DM the thing is that his slow, he needs to be paired with a skilful player that's fast so when he loses the ball, he can track the player while Casemiro will mark the free player that he intends to pass the ball to. Look at the game against Fulham, when Amorim removed Casemiro, that was when the deep in the midfield was totally open because nobody to do the dirty work in that position. For those people that still thinks Manchester United doesn't need defence and midfield, I hope they are watching what's happening to the team in this past two matches.