Messi isn't the only person bearing the blames. Neymar and Mbappe are also doing the same. More blames will be coming because myself I also blame them. Messi's case is different, this is because, at his age, we ain't expecting many extraordinary things from him like He always does when in Barcelona. Secondly, Messi is doing his best to make sure that his younger stars/ Colleagues ( Mbappe and Neymar) receive enough assistance and supports that they deserve from him, with this, much is done by Messi but little will be seen. So as a significant figure, you can't escape such blames.
PSG win and lose as a team and no single person should be blamed for their success or failure in a season. Messi, Neymar, Mbappe are their attacking players who are mostly responsible to score goals for PSG and partially contribute to their winning chance. However they are not god and can not bring PSG to winning in all matches if they don't have support from midfielders and defenders.
In return, midfielders and defenders need support and contributions from those players in defensive efforts which will help them to reduce pressure on their defense system and goalkeeper. Generally, their players must do attacking or defensive task as a whole team not as a single player.