It's interesting indeed, because even though Bayern Munich this season will fail to win the Bundsliga trophy but yes, basically Bayern Munich still has good quality if we only compare Bayern Munich with Lazio. But yes,theresult in the first leg was a surprise because apart from losing with a score of 1-0, but in fact that Bayern Munich also had no shots on target at all in the first leg. Therefore, in the first leg it can be concluded that Bayern Munich played very badly or perhaps, Bayern Munich underestimated Lazio too much so that Bayern Munich was not in good focus in that match. So yes, with a very bad result in the first leg, then Bayern Munich should produce a better result in the second leg because Bayern Munich will also be playing at home.
It seems to me that there should be no such thing as underestimating an opponent at the Champions League playoff stage ,any team that was able to pass the group stage should by default be an opponent that is worthy of respect. Bayern simply were not ready for Lazio to play so well in defense, I think this is the main reason. But Bayern have the second leg where they will have a chance to turn things around, the difficulty for them may be, that their defense is not the best, and if Lazio can score again and try to play just as well in defense then there could be a sensation.
We must not forget the surprises that are always presented by Italian football clubs. Last season there were even 3 clubs from Serie A who were able to proceed to the quarter-finals. So it could be the same this season. Even though Bayern is actually much stronger than Lazio, which is not even consistent in Serie A. But the mentality of the players from Serie A clubs is actually always superior. This is what makes clubs from Serie A always succeed in surprising all the clubs in the UCL.
However, in the second leg, Bayern will probably be superior in many aspects. In terms of squad depth and being the host, Bayern will dominate the match quite well. But we also don't know whether Lazio will focus on building a strong defensive fortress again or whether they will continue to play offensively. But I think Lazio will try to maintain the advantage they have by defending and occasionally counterattacking. Because Lazio must also realize that if Lazio plays openly and attacks then it will only endanger their own defense.