I don't think its because Newcastle appears weak, but because Manchester City performance has started to improve. You can see when Newcastle took the lead in the first half with 2 goals, this is enough to proved that Newcastle is not a weak club and Kevin De Bruyne made his contribution by contributing 1 goal for Manchester City. So Manchester City are still quite confident with their current performance when playing away games, Manchester City is starting to become the strongest again and is more ready to fight for the title this season and defend the title over the last few seasons.
Yes, the competition between Liverpool and Manchester City is getting hotter because Liverpool also want to break Manchester City dominance in the last few seasons and they are also ready to compete for the title with their performance being quite consistent to date. Liverpool will take advantage of the situation when Manchester City is still lacking stable with Haaland not yet at the club.
Kevin De Bruyne's entry in the second half really had a big impact on the Manchester City team so they managed to turn things around and win. Kevin De Bruyne is truly an extraordinary player and with his recovery from injury, Mancheter City's performance is much better with a big contribution. which was given by Kevin De Bruyne.
And for Newcastle, I think there is also an improvement in quality compared to some of their previous matches, but Manchester City is a strong opponent for them and overall Man City's quality is much better than Newcatle's, so this defeat is quite natural.
However, if you look at it as a whole since the start of the season, with Newcastle's decline compared to last season, I think there are quite a lot of things they need to improve if they want to compete again at the top like they did last season.