Arsenal lost both in the league and the Champions League.
I don't think this point loss and defeat is good for Arsenal because they could have found morale in this match.
It is not strange if Arsenal loses 3 points when it is nearing the end of the season. Because in fact they are starting to lose their fighting spirit in the League after the trophy was won by Liverpool. There is nothing Arsenal needs to do anymore to chase the top of the standings.
Many were of the opinion that the reason why Arsenal lost their game in the premier league yesterday was because they were focusing on winning their game in the champions league, but then, it's very unfortunate to learn that they also lost their game in the champions league as well, it's nothing to be surprised really just as you have said, for over the seasons, Arsenal have been known to start dropping or losing points as soon as a season is coming to an end, very disappointing though but this seems to be becoming a normal thing to them.
On the other hand, Man United as usual is not interested in performing optimally in the League, they seem to have given up and want to stay focused on playing in the Europa League. Brentford is now leading 2-1 and in the second half will they add one more goal or Man United try a little seriously.
I doubt Manchester united will be able to beat Brentford who as we know are currently leading with 2 goals to 1, I am not currently watching the match to tell how Manchester united is playing but my honest prediction is that they will likely lose.