It would be very naive if Madrid did that because in the end we also cannot assume that Bayern is an ordinary club, especially with the release of the Bundesliga trophy at this time, so the goal is the Champions League because it is the only way for Bayern to save their face so surely they will try as hard as possible to get good results so it is wrong if Madrid considers Bayern underestimated in the semi-finals this time.
But for now with Madrid winning against Manchester City some time ago, their probability has increased and they are the favorites in this competition.
I personally still feel that until now Madrid is the favorite for the Champions League and indeed I feel that now is the place for Madrid to get their 15th trophy.
There's no reason for Madrid to underestimate Bayern
They have always been one of the most dominant team in the UCL in recent years so caution would be employed while playing them no matter their form.
Madrid can be considered a favored child in UCL
No matter their form
They always are the likeliest to win the trophy and who ever manages to win them has already won the UCL.
At this point, I will say Real Madrid are going to get this title. Although I know that in this stage of competition, no opponent can be underestimated, with the kind of performance Real Madrid get now and the kind of performance they showed in their previous match again, Manchester City vs. Bayern Munich will no longer be a very big challenge for Real Madrid, so we will say they won’t get the title. It's not that I’m underestimating Bayern's performance, but Real Madrid are stronger than them currently.
Even if Bayern Munich dominates the Champions League every season, I can say that this season I see something different because there are some signs of weakness in them, and this will give Real Madrid a higher chance of winning the Champions League this season.