Let's get over with this now! Arsenal has no chance of winning the Champions League. That'll be considered an expensive joke. They should focus on winning the Premier League this season and not prioritizing a competition they know quite well they can't win.
They've had a remarkable season last season, so I expect them to use that energy and motivation towards getting the Premier League job done.
I didn't expect them to drop points off against Lens though, they shouldn't have lost that game. They should be very focused when they face Sevilla ahead. Sevilla now has a new coach, so they should expect something different and tough.
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.