It isn't a very surprising thing to me. Maybe people are surprised with PSG's drawing with Monaco because of being used to seeing PSG win most of the time. But when we examine the head-to-head games between PSG and Monaco we can see that the results are not much absurd. Because Monaco are still not a very weak team against PSG even though there is a visible difference. Messi was not good at all in this game by the way. I didn't see his contribution much and the goal they conceded came after he lost the ball as well. Mbappe could have been the hero by the way if he didn't miss a big opportunity to win the game.
Monaco is not a weak team, the previous season Monaco was in the top 3, meaning that Monaco is not an easy team to beat. So as you said it
shouldn't be a surprise if Monaco managed to draw with PSG. The problem is that Monaco started this season not too well, even Monaco's previous
match was very bad. When compared to PSG who achieved amazing results in the previous 3 matches, this is what finally made some people surprised
that PSG failed to win against Monaco.
I agree Messi's performance is very bad, because Messi lost the ball, Monaco could finally take advantage of the counter-attack and score a goal.
Mbappe also played too selfishly, so in that match I didn't see the good cooperation of the 3 PSG forwards. Very different from the previous 3 matches
the collaboration of Messi, Neymar and Mbappe was very good. Hopefully Galtier learns from PSG's failure to win, and in the next match PSG can show
a better game. Moreover, PSG does rely on their 3 front players, so the three PSG forwards must be able to work well if PSG want to get back to
positive results.