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The Champions League competition is very mentally draining so PSV can easily go down or vice versa. It depends on whether the players are ready or not to face a club as big as Arsenal which is in top condition. However, PSV's motivation is still quite high and they don't want to slump at the start of the season. I will not doubt PSV's performance in the last few matches which seems to produce solid matches. On the other hand, Arsenal also needs to reconsider, Arteta cannot make the wrong decision again because his return to the Champions League must be utilized well. At least getting through the group preliminary round in my opinion will not be too difficult when compared to other groups.
Apart from Group F, there is no group that will be really tough for the favorite team. Arsenal are the favorites in my opinion, so they shouldn't disappoint because I know the quality of the team at the moment. PSV of course has a chance to qualify, but I'm sure other teams also have the same chance.
I agree that PSV is also good to look forward to, but who would have thought that Sevilla who are currently not in good shape might be a surprise. Sevilla cannot be underestimated even if they are not in good form in La Liga, so 3 teams between Arsenal, PSV and Sevilla are likely to qualify for the next round.
You probably mean Group B. Because Arsenal are not in Group F. Group F teams are PSG, Dortmund, Newcastle and AC Milan. And Group F is the toughest group in this year's Champions League. Every team has a chance to qualify for the knockout rounds.
If we talk about Group B, there is no way to say that other teams in this group are weak except Arsenal and PSV. Sevilla and Lens are strong enough teams. However, the recent performance of these two teams is very bad. This is why PSV and Arsenal are expected to top the table. And these two teams will qualify for the next round. Sevilla and Lens are strong enough. If they can sort out the problems within the squad, it will not be easy for PSV to qualify for the next round.