It is more than just a lack in consistency and yes Arsenal was consistent, but some other team was more consistent than them. That makes the difference. Arsenal scored 9 points last season, do you think that a team scoring 89 points would reach that number without being consistent? But sometimes the problem is that there one team being more consistent, which doesn't make Arsenal inconsistent.
In 2022/2023 they had 84 points and it was not enough. In 2023/2024 they had 89 points and it was not enough. In my opinion I think both results are good, but playing against Manchester City makes this look inconsistent because most of the time they have raised the bar so much that unreal performances were necessary to win the title.
Now it is Liverpool which is probably getting close to 90 points.
I agree what you are saying that Arsenal problem is not that they are not consistent but that another team is even more consistent. You are right that Arsenal got a lot of points in last two seasons 84 and 89 which is very good but not enough to win championship. This shows that Manchester City has set very high standard so other teams have to play extremely well to compete with them. Now.it looks like Liverpool is also trying to get a lot of points almost 90. This kind of strong competition is what makes Premier League so exciting.
Which is Liverpool team and they are still consistent till now, because their head coach is doing what other head coach couldn't do to make the team consistent in winning in the premier League competition and other competition too. Arsenal has played well over some seasons now to maintain second position but to win the premier League title is the challenge they have now, because they are still maintaining second position over some matches now. I have watched many matches in this premier League competition, I think Liverpool is going to win this premier League title this season.