Barcelona seems strong and a good team but, they havent played again a strong team in the short term, so we really dont know if they are really strong or not. This can be the first challenge for them against Bayer Munich, and it hink Bayern can win this match for 3-1 or something like that.
Lewandowsky can score against his former team.
I would say that they are strong enough to beat Bayern but at the same time the situation is too close. Normally I would give the win to Bayern, because Barcelona has been bad and they are still not recovered yet because they may have a good roster but they need to show and proof they are ready again for a long time.
At the end of the day, we should be looking at the current situation of Barcelona as unknown, they may look good but they are not tested just like you said. Which is why I am expecting them to have a season where they won't really have any type of problems big time, but not have a great season where they win it all neither.