I don't think Arsenal becomes the favorite here. Although they are playing well in EPL, it can't guarantee anything for the match in UCL.
You can see Arsenal very difficult to qualify against Porto. Arsenal needs to play until penalty shootout. This indicated that Arsenal isn't so strong, the position in the EPL can't describe how strong Arsenal in UCL. If Arsenal is quite strong, they must be easy to beat Porto.
It is different with Bayern Munich. They looked quite good in Leg 2 against Lazio. Bayern Munich have no problem to defeat Lazio with 3 goals. If they were unable to win in Leg 1 against Lazio, I think it can be the impact of Red Card got by Upamecano. Well, as long as Bayern Munich can play with their main lineup, I'm sure Bayern Munich can beat Arsenal. It is not only about the record, but Bayern Munich squad quality also seems better over Arsenal.
If you compare the leagues and recent games, Arsenal seem to be the favorite. On the other hand, Arsenal have not performed well in the CL in recent years or have not qualified at all. Many Arsenal players are less experienced internationally than Bayern's players. That could end up being a decisive advantage in a knockout competition. Bayern also have the advantage of being able to concentrate more on the CL, while Arsenal are still in the middle of the championship fight. I favor Bayern in this match.