Arsenal had failed to maintain their consistency due to injuries and most likely fatigue too as the same players were the ones playing all the time. But I don’t really get what you meant by Arsenal not having a winning mentality. I think they’ve got a winning mentality and that’s why they had been leading the league table for a while.
One of the reasons Arsenal failed last season was due to Arteta poor management in the crucial stages; and somehow it passes everyone radar. Arteta as arsenal boss made some changes that disrupted Arsenal game play and kickstarted the poor performances. One is rushing Jesus back from injury, then benching Fit and firing Trossard for the just getting fit Gabriel Jesus; second poor decision was refusing to drop or rest Saka despite heavy and obvious burn out from the right winger. With better squad depth; i hope he improves in that aspects.