In fact the Europa League this season is more interesting than last season. Barcelona did fail in the Champions League, but don't think they are weak just because they lost to Bayern and Inter. I will look forward to their fight in the Europa League this season, and it would be better if Barcelona met Arsenal sooner. :v
They failed 3 per 4 matches against Bayern and Inter Milan, got only one point from Inter Milan and 0 point from Bayern. With this performance, their two wins against Plzen are non sense for them in the group.
Losing 3 per 4 matches and you said Barcelona are not weak enough

About Arsenal, they are good but I don't think they were very dominant in the game against a strong team. The fact that Laliga teams tend to be strong when they meet Premier League teams, that's history.
La Liga have worse performance in Champions League in recent seasons. The success of Real Madrid in the past season is like the success of Mourinho and Inter Milan years ago, but they don't change a fact about decreasing quality of La Liga and Serie A. Serie A after the successful season of Inter Milan was falling down in Europe and I believe La Liga are facing a same issue.
Indeed. Barcelona may be one of the favorite teams to win the Europa League title. However, Barcelona seems not really well when they are playing in international matches. In the last season, they failed to reach the final, they are defeated by a smaller team. Man United, Arsenal, Ajax, and Juventus probably will be strong opponents for Barcelona.
You forget about Roma and Mourinho, they can be another strong opponent for Barcelona in Europa League too.
On the other hand, smaller teams like Lazio, Real Betis, Real Sociedad, or Monaco can defeat Barcelona as well, if they are not seriously to plan a proper strategy against them. So, there will be always a chance for Barcelona to fail again this season, we cannot underestimate other teams in Europa League. We often saw a surprise in this competition.
I don't consider they are smaller teams than Barcelona. About tradition, I agree they are smaller but if we only compare them in aspect of their strength in this season, they don't have big differences. If Barcelona failed to beat Inter Milan and were only able to beat Plzen in their group, they will have so many difficulties if playing against any club from Man United, Arsenal, Ajax, Juventus, Roma, Lazio, Real Betis or Sociedad.