I think now that Arsenal knows they are going to play against Bayern Munich, you are worried because of the past games because now there is a chance for Bayern Munich to score five goals again against Arsenal. Except for the recent fiend match they had in ~5 years ago in which Arsenal won the game with a 2-1 result. In the other games they had, Bayern Munich won the game with a 5-1 result, and scoring five goals is not something normal at all.
Now Arsenal is not in a bad situation Bayern Munich is under pressure because of losing the Bundesliga title and they have to beat Arsenal, I'm waiting to see how Bayern Munich and Tuchel can perform against Arsenal.
Yeah both teams are in different situations this season we can't compare their performance based on last season's matches and each team has its own advantages, here in the first leg Arsenal are very favorites to win then in the second leg of course Bayern Munich are the favourites well as I said before the goal difference will determine who will go to the next stage. One thing I note is that Arsenal is on fire in the Premier League while Bayern Munchen are not doing much better due to some recent bad results..
The performance of a soccer team can change drastically from year to year, so even if the recent matches between two teams can be taken into account, at the same time we cannot really give them too much weight, and instead we must consider the current performance of the teams, the quality of the opponents they have faced, the results they got, the injuries of their key players and even the amount of minutes each one of those players has played recently, in order to get a better idea of which team between Arsenal and Bayern Munich will make it to the next round.