Group B is an easy one for Arsenal. They can even win all of their matches if they concentrate on all of them equally. They might be a young team now but they are still way more powerful than all of their opponents in this group. The only competition might be made by PSV against them but I think Arsenal wouldn't struggle against them too much either.
This feels like no different than a Europa League group honestly. I remember Arsenal and PSV in the same group there before.
When it comes to Sevilla's chance in this group I think they will finish behind PSV if they don't improve their current performance.
At least, if we consider the results they have in their respective leagues at this moment, then of course Arsenal remain the favorites to win group B. Because after all, teams like Sevilla and Lens at this moment they are also experiencing bad results in their respective leagues. Even Worse, Sevilla and Lens at this moment are stranded in the relegation zone in their respective leagues. But about PSV, although PSV remains in the upper zone in the Eredivisie standings, but at least the Eredivisie and Premier League levels are different, and that factor also makes us believe Arsenal can have good dominance in this group B. But even so, I personally feel that Sevilla and PSV can still have good results too in this grup, and of course it is still not easy for Arsenal to be able to win consecutive wins in this group.