Bayern are not favorites in the Champions League right now, but they are definitely one of the contenders. Everyone is trying to remember Arsenal's amazing results in the Premier League, but the Champions League is a different tournament and Bayern is a team of a completely different level. As far as I can compare these opponents, it is clear to me that Bayern are superior to Arsenal, despite all the difficulties that the team has had to go through this season. Besides, every team has its downturns, and it may be good that Bayern went through this difficult period earlier, as far as their recent results are concerned.
The favorite to win the Champions League title is clearly between Real Madrid and Manchester City. Bayern Munich is the 3rd option if one of Real Madrid's or Manchester City is knocked out of the Champions League in the quarter-finals. Bayern Munich has more experience than Arsenal, so it's natural that many people favor Bayern Munich in the match against Arsenal. In fact, I saw in posts on social media that many people mocked Arsenal because they were beaten by Bayern Munich in their last meeting in the Champions League. With insults like that, Arsenal should get up and take revenge this season because their performance is very good in the Premier League and Arsenal's attack level is also quite strong so against Bayern Munich Arsenal must be better prepared.
The chances for both of them to reach the semifinals seem to be the same, Bayern Munich does not completely have a bigger advantage because Arsenal also appears at full strength so Bayern Munich must be aware that Arsenal is now different so the possibility is big that Bayern Munich will experience big problems when facing Arsenal and vice versa, English clubs Arsenal and Manchester City are making good names in the Champions League this season.