Coutinho was actually pretty good that first half season with us, when he could not play in CL, which makes it pretty puzzling how he fell out with both manager and dropped in his performances his first full year.
Just some comparsion stats:
17/18 season - 18 games 8 goals 5 assists, 1303 minutes played, so basically assist or goal every 100 minutes. Thats is top quality level
18/19 season - 34 games 5 goals 2 assists, 2019 minutes played, so assist or goal every 290 minutes and a mental wreck.
Although he is not a regular with Bayern, his stats this season for Bayern are close to what he had with us in first half of year, then again, he has not really played vs top opponents in Bundesliga, so it is a bit flawed.
I think Coutinho is mentally pretty fragile and considering our squad at the moment, he just does not fit as he would be additional emo in locker room. His level is also very inconsistent and i do not see where he would fit in Setiens gameplan (he would still be better than De Jong or Vidal as LW though) as he is probably best as attacking midfielder drifting in from left and as long as we have Messi (who does the same thing from right) we do not really have a need for that position.