I wish I knew what the odds were for Osasuna to win with a handicap of -2. Probably something around 50.0

As for rotation, Flick changed most of the defense/midfield too. I wonder if he really believed that it would be an easy game and he could experiment here without problems?
Update: Yamal scored a goal, but the score still didn’t become decent after that, 4-2 is too much.
Well the handicap you are talking about was indeed -2.5 at the time of you writing the post. It must have been huge. Barcelona winning the game was like 1.55 or something and Osasuna was around 7.0 or 6.5 or so. Put on top of that a -2.5 handicap, that was definitely huge.
As for the rotation, I think it was bad by Flick to exaggerate like that. When I saw how many players he rotated, I already had a feeling that Barcelona is risking a big chance here to be the big winner of this weekend. Real Madrid and Atletico stealing points from each other and Flick thinks it is time for rotation.
You guys recall that Flick was giving a press conference where he said that he should have given one player who got injured more breaks? Maybe this was his response to his own statement that day.
I don't fully understand his decision as the Champions League game shouldn't be that hard. It's not like they are up against Inter Milan or another team one that level. Young Boys Bern next and then he goes for such a rotation against Osasuna, which by the way shouldn't have been underestimated in the first place.
Young Boys beat Galatasaray twice to get into the Champions League, apparently Flick (quite logically) assumes that after the defeat to Monaco even a draw with Young Boys will be a serious blow to Barcelona's prospects in the Champions League. Maybe not even in the tournament sense, Barcelona will score enough points to get at least into the preliminary playoffs, but in the psychological/mental sense.
The problem with rotation is that it always comes at the wrong time when the result is not achieved. If Barcelona had won today, no one would have criticized Flick for experimenting.