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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.
You are right that Sevilla and Lens are teams that cannot be underestimated even if they are not favorites to qualify. PSV and Arsenal also haven't proven anything to us that they can beat their competitors in the group without any problems, however, the performance of the two teams in their respective leagues might be used as a benchmark for analyzing opportunities.
In group B the favorites are Arsenal and PSV, but as I said, Sevilla and Lens also have the opportunity to win points in every match that will await them in the group stage. We can only speculate, but it all depends on the performance of each team.
Regarding Arsenal in group B of this tournament, they gave the list of players they want to this tournament but the sad thing for Arsenal in this Champions League is they can't use they player, Jurrien Timber, while this player joined Arsenal for 40m from Ajax but this Dutch player is injured hardly and they didn't add his name for this Champions League. There is even the chance for him to lose the whole season.
