Being on course to X pts is just a way of speaking, it shouldn't be taken too literary. To say that Arsenal are on course to win X pts is to project tendencies from the first 17 games onto 38 games. And that's highly problematic. Getting 90 pts is anything but easy, even on the basis of 44 pts after the first 17 games. Remember, Arsenal have won 90 pts only once (2004), and the league was less competitive back then. Martinelli and Saka are top talents, but they ain't Henry. It's not impossible for Arsenal to get 90 or even 95 pts. But it's not as likely as it may seem after the first 17 games.
Just as City dropped 5 pts in 2 home games vs Brentford and Everton, so will Arsenal drop points unexpectedly. Again, they don't outperform City in terms of creating and conceding chances. Nobody expected Watford to twat Liverpool 3:0 after Liverpool dropped just 2 pts in the first 28 games in 19/20. They were on course to 110 pts back then. And then dropped 13 pts in the last 10 games. It's not like they didn't want to break City's record of 100 pts. Form comes and goes, often unexpectedly.