Claudius
I actually agree that we fell apart mainly after Partey and Saliba went down, and we did not have capable backup (I mean, i liked Rob, but he was a big reason we tanked last year). This year, in theory, we have much more capable backup should one of the core players get injured.
But we were also ahead in some of those games, and fell apart during the game and dropped points. And part of that is mentality (and yes, part is personnel). You are right that there are many factors, but for a while now, Arsenal has been known as bottlers, with good reason, as we often have done it. It seems less of an issue this season, but the last 10 games of the season will really show if we have the right stuff.