If I'm not mistaken, the last time PSG didn't participate in the main stage of the Champions League was in 2011. It's unlikely that anyone in the club remembers those times, since PSG then got used to dominating Ligue 1 and getting into the Champions League directly. This has created a certain champion mentality in them, but I can't say that Arsenal's is much worse. After all, the EPL is a highly competitive league and Arsenal have become accustomed to fighting for the title in recent years, anything less is seen as a failure.
Based simply on the balance of league strengths, I assume that Arsenal are clearly stronger than PSG.
When it comes to league competitions, I think PSG have more success than Arsenal for the past years, the only good record of trophies Arsenal has in the EPL is the FA Cup which they've won more than any other team and that was in previous times, but recently they've got no notable trophy to their name and are just runners up for two consecutive season while PSG have been very dominate in their league for decades and counting and even when they didn't win they their league, they still finished in the top 4 and qualified for the Champions League effortlessly so PSG has more an better Champions league history than Arsenal. Well it's not always about history cause presently this current Arsenal team is a threat to any big team, their squad is not looking very threatening on the papers but on the pitch they're full of wonders and player very good football, all thanks to Mikel Arteta.
I think that Arsenal of the last three years would have won Ligue 1 without any problems (even with PSG playing there) and PSG would hardly have entered the top 4 of the Premier League with any of their star squads. This is subjective of course, but judging by the bookmakers' odds, they don't believe in the French champion. It's a pity that this is a group stage game, I would like to see the result when the teams play at full strength.