I'm not surprised at all that Arsenal is a favourite against Bayern. Arsenal's stats in the Champions League group stage look better than Bayern's. Although Bayern has earned 16 points, and Arsenal 13, I think the German team had an easier group. In terms of average goals per game scored and lost, the stats suggest Arsenal is better in both offence and defence:
Arsenal: 2.7 scored and 0.7 lost
Bayern: 2.0 scored and 1.0 lost
Do the stats from the group stage really matter in this match? Inter Milan has better stats than Atletico Madrid in the group stage, but Inter lost against Atletico Madrid. It's a surprise to anyone who fully trusts Intermilan to win the game. Bayern played so poorly in the Bundesliga, and it can be considered the worst performance in a decade from Bayern, but it can still potentially win against Arsenal, too. I think the thing that matters a lot is the composition of the squad.
The same stats for league games are at a similar level, but it's hard to disagree that the Premier League is much stronger than the Bundesliga.
True, the arsenal has always very often lost against Bayern, even since a decade ago. it means that if bundesliga team can't be underestimated.
That being said, it's a bit concerning that Arsenal struggled to get past Porto, as they needed a penalty shootout to go through, and I think Bayern is a better team than Porto.
Bayern is a 1 billion team and it's far stronger than porto. The last time Bayern beat Arsenal was 10-2, as the final aggregate happened in 2016/2017. I think that history will repeat itself again even though the majority of people favor Arsenal, but I think Bayern is still strong enough to beat it.
It's time for Tuchel to prove his worthiness as bayern Munich's coach. Things will not be going so well for arsenal.