Arsenal are in good shape but they also know their limits this season. You're correct, Mikel Arteta should tend to concentrate on EPL other than distracting the team in UCL race. Gunners is yet to face any big team in UCL this season, they meets and records thrilling victory against these average teams. EPL race would become easier and possible for them to win and not elite competitions were there's presence of tough competitive clubs. Winning UEFA Champions League is an impossible task for the Gunners, after been absent in the elite competition for long term.
Maybe this season Mikel Arteta will make a difference to last season where Mikel Arteta will also concentrate on the Champions League apart from continuing to concentrate on the EPL. Although in general I am not sure that Arsenal will progress smoothly to the next round, but for the round of 16 I am still quite confident that Arsenal has a better chance of qualifying. Because in group B there are no big, stronger teams, so it is more possible for Arsenal to qualify for the next round of the Champions League.
Arsenal's performance this season is much better than last season and in Group B there is no strong opponent for Arsenal so I think there is no reason for Arsenal not to qualify from the Group even though they have already suffered their first defeat against Lens in the second match, I think it is not big problem.
I remind you that if arsenal was not playing in UCL last season. Arteta's club was only playing in europa league and it was also failed. Arsenal is still on the group stage but it's still potentially to leave from the group as well.
Arsenal is not that strong as you think when it was aboue competing in the european competition. Look at how arsenal got win streak till weeks 33 but it's failed to get EPL.
Every team will definitely focus on their UCL matches because this is the most prestigious competition in Europe, and with the quality that Arsenal has this season, it is very possible for them to go further in the UCL this season.
Arsenal is getting the easiest team in champion league. It will be a shame if this club will not be able to pass the group stage to go to the next round. Arsenal fans are putting their hopes to this club but i can't see that in the future if arsenal will be losing and back to the emirates stadium.
Arteta needs more than skills owned by its players to win UCL. The club needs to have everything to get its first UCL trophy.