Two things conspired to bring Arsenal to its knees ,one ,an owner that sees Arsenal as a cash cow .Two the loss of Carzola.
Incidentals like a poor back room team,poor fitness ,poor basic. Training, arrogance from poor players like Xhaka who lacks drive and creativity.. and a lack of discipline .
It's not a team it's a collection of individuals.
Small things like..the opportunity lost due to who takes the throw in, the game stops until ,as an example ,Bellerein ,comes to take it. Lost advantage.
Passing back to the goalkeeper and putting him under pressure making him boot the ball upfield into the arms of the other team.
I am sure you can all list other things ,as I can .
Get rid of an inept back room team ,we might avoid relegation.