Due to the odds that the gambling sites are offering in Bayern Munich against Barcelona, it's obvious that the match will be tough. Of course, the H2H doesn't guarantee anything in this game because this is not the mighty Bayern Munich that we knew years ago, Bayern Munich has included new faces in the squad, and we should not think that Bayern Munich will beat Barcelona because they previously beat them 2:8 or Barcelona hasn't won any of their last five meetings, Barcelona is in great shape this season, if Barcelona is going to lose the match, the bookmakers won't offer the odds as they understand what they are forecasting as well.
On the other hand, Bayern Munich is still not in top form to beat any big team since last season, and they have struggled to play against any big team since last season, I am not expecting Barcelona to lose to them so easily, and Hansi Flick is an experienced manager, he may come up with a strategy to defeat Bayern Munich at home.
The results of past head-to-head matches should not be considered to select the favorite team this season. If we only consider the results of the head-to-head matches, then without a doubt the Bayern Munich team has to be considered as the favorite. I can't remember the last time I saw Barcelona win against Bayern Munich. Barcelona have lost their last 6 matches against Munich in the Champions League. Considering this aspect, the Bayern Munich team should be considered as the favorite in the next match as well.
But you mention an important point. Although Bayern Munich has been in great form this season, the team has not won against any of the big teams. Bayern Munich failed to win against Leverkusen and Frankfurt in the Bundesliga. On the other hand, Munich lost 1-0 against Aston Villa despite a huge 9-2 win against Dinamo in the Champions League opener. So Munich has a big chance of losing points against Barcelona. Because the Barcelona players are in a good rhythm at the moment. Also the players are very confident.