I don't remember Arsenal having any good success in the Champions League. Almost 20 years ago they played in the final against Barcelona and lost. Then a few years ago they played in the Europa League final against Chelsea and lost too. The younger the squad, the less experienced they are. So it seems to me that they will fail again this season.
I don't think Arsenal will fail again this season with their young squad, because of the several failures Arsenal have experienced in previous seasons. Of course this has been a very valuable experience for Arsenal so maybe next season Arsenal will make better changes with their young players, but if Arsenal still fail again next season. This means that Arsenal must quickly find their mistakes so they don't fail repeatedly in every season.
for Arsenal performance, I have no doubt that this summer Arsenal has had a very good performance and has improved very much, but to be successful in the champions league, I think I am a little doubtful. because Arsenal have to get past rival teams like Man City who are currently in a very strong state and also Real Madrid who are currently aiming hard to win the title after failing last season.
so its not easy for Arsenal to have to go through this big team and if they fail again to get the title this season I think the mistake is the strategy used by the coach himself.