Bayern Munich doesn't have strong defense and it is same with Barcelona but these two clubs have good attackers. However, I see Barcelona having advantage of Bayern in this match because they are playing in Nou Camp and Barcelona have sharp attackers and quality finisher than Bayern. Lewandowski have no choice than to play against his former team. It will be his pleasure to score against Bayern.
It is known that Bayern Munich are always winning Barcelona whenever they clash for quite some times now. But let's not use the past to judge the future because things have changed presently and there is no assurance that history will repeat itself again.
For now, Barcelona as the host will indeed have quite the advantage. Because mentally the Barcelona squad should be more favored because they are playing at home. even though you said you don't need to look at the history of meetings between these two teams to judge their upcoming match. But still, the head to head between these two teams is very interesting to discuss. because Barcelona always loses when they meet Bayern. Both in home and away matches over the past few seasons. And the last time Barcelona won against Bayern was in 2015. And yes, that was a long time ago. And it's possible that in the end Barcelona will win again in this meeting after always losing for so long. Because I see that Barcelona's current style of play is quite different thanks to Hansi Flick. So the meeting between these two teams this time seems to be more difficult to predict. I might prefer to just favor the home team.