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I agree with your opinion that Ligue 1 is one of the weakest leagues among the top European leagues. In fact, we can see how dominant PSG is in Ligue 1 and how other teams are unable to compete with them. This is different from other top leagues such as La Liga, Premier League, Serie A or even the Bundesliga which have rivalries in competition. But I think PSG is not a weak team when compared to teams from other leagues. PSG dominates Ligue 1 because other teams are weaker than them, but I see PSG can also become one of the best teams in European competition. PSG made it to the semifinals in the UCL and that shows their level. It's just that they have never been among the favorites to win the UCL in my opinion.
I agree more if you call Ligue 1 a farmers league, the other clubs are just complements without being able to compete with the strength that PSG has. PSG always dominates every season, even before the season starts we can guess who will win the Ligue 1 title race. Due to the very weak competition in Ligue 1 making it difficult for PSG to compete in the Champions League, PSG will be surprised when they face another strong team because in Ligue 1 they have never faced a club whose quality is equal to theirs.
PSG is an elite team, the quality of the squad they have always places them in the group of favorite teams to win the Champions League trophy. Their failure to win the Champions League was because the players did not have the mentality to win the competition. This was because the PSG players' mentality was not honed in the domestic league because every match they played there they were always able to win easily.