I think Arsenal on the contrary now is the time to become consistent outside the EPL, they are strong enough and hold serious competition in their home league, which can't be said for Bayern. Maybe Arsenal will take advantage of Bayern's position and still be able to go further in the 1/2 of the tournament
If Arsenal is going to beat Bayern Munich and take revenge for all the beatings they have received in the hands of the German champions, then the time is now, they might never get a better chance to beat Bayern Munich. Tuchel's men are really struggling and now their only chance of lifting a trophy is the CL, but they are faced with a huge test in Arsenal.
If Arsenal are to progress to the next round, then they have to beat Bayern at the Emirates. Bayern Munich might not be in form, but beating them in the Allianz Arena is a tough proposition, thus Arsenal need to take the initiative and win in the first leg, so they can at least carry a win into the second leg in Germany.