Arsenal's performance against Lens was not bad. There was some strategic mistake so they lost. Arsenal's overall performance in this match was very good. I don't think Arsenal will make the same mistake again. Arsenal team is strong enough. Sevilla's performance, on the other hand, has been weak and erratic. I don't think Arsenal will make any mistakes against this team. If Arsenal's defense can perform a bit better in this match, I think they can beat Sevilla. Sevilla team can be considered as the weakest team in Group B.
Arsenal was almost making it but lens was too strong when it was playing at home. Arsenal has been trying so hard to get at least 1 point but it was failed. I would not even blame this team caused by arsenal has been trying its best to get three points against lens.
The upcoming match is going to be a tough game. Arsenal may also be able to measure how strong its opponent is through seeing the match between arsenal vs real madrid.
I would rather call PSV as the weakest in the group compared with sevilla. Sevilla has been also recruiting a new coach and the club may also be able to change a bit compared when mendilibar was still there.
Sevilla was europa league winner and arsenal failed last season to win it. That's why arsenal must be careful even though sevilla was not in a good shapes due to the various mistakes.
The defensive line still becomes the main problem owned by arsenal. The team needs to fix this too.