Mbappe is a young fantastic player, and I think any club that owns him will be very proud of him. They won't be happy to see a young great player leave their team, either, because it's really uncommon to find a young player with his level of skill on the market right now. I think PSG understands the worth of mbappe in the team, which is why they treated him with such respect. I might even argue he deserves it because he has been giving it his all for PSG, which has greatly aided the club's success.
If I have to say that I don't think anybody will underestimate Arsenal in the next Champions League with the performance the club showed last season and the way Arteta has built the team by bringing quality players to the team, I believe that should be enough evidence for anyone that Arsenal will perform well. With this Arsenal squad, I am expecting them to be a great team next season with many achievements. Arteta is a great coach, and I believe that he has learned from his mistakes last season, which is why he is trying his best to bring in strong and determined players, not just players by their names.