You’ve essentially negated your point that changing the style of play to accommodate one player is highly damaging by using PSG as an example and listing three players. We all know that accomodating three players is a completely different beast to one.
Also, in what way can you prove that he has messed up the team balance? I’ve watched City loads, and they’re still creating a lot of chances in most games and are the highest scorers in the league. Would you be making this post if their defensive players like Cancelo, Stones etc, guys whose performances have absolutely nothing to do with Haaland, were not playing as poorly, or at least inconsistently, as they have been this season?
I have negated nothing as these players didn't arrive at the same time, and while I think Messi is a great addition in terms of creativity, his lack of activity makes the balance of the team weaker.
Most of City's players are totally average defensively and they only managed to be stable because they were all working as well oiled cogs. Even Pep says so , Bernardo isn't a good defender, Gundogan, Rodri, Foden etc. aren't good defenders, but they defend well as a tight unit and he doesn't have a Fernandinho anymore to cover for mistakes. They changed a cog in the machine and now it's harder for them to block transitions when they occur.
I think it's pretty obvious to anyone who watch the game that performances were affected by these changes. Either Haalands manage to dominate his box and they can score 6 goals (which they already did last season) or he doesn't and they look uninspired and struggle to score 1-2 goals against very average teams. It reduced the importance of Bernardo Silva, Foden, Cancelo etc who used to be very important players for City.
So now you might think that these players having a drop in performances has nothing to do with Haaland (well not really with Haaland but with the changes made by Pep) but I highly doubt that Bernardo, Cancelo, Foden and even some defenders randomly got worse at the same time, exactly when Haaland joined the team. What a coincidence it would be.
On the other hand, KdB is more than ever the key to City's offense, he's constantly involved and he managed to sustain a very good level, but that's probably another coincidence.
They used to be able to fire from all cylinders and crack low blocks pretty easily, now they struggle far more often against low blocks when Haaland is busy with defenders. There's no other significant goal contributions from other players and even Foden seems out of gas.