Even though Barcelona is playing in the Europa League it is not a guarantee that Barcelona will be easy and also, last season even Barcelona were eliminated quickly by Eintracht Frankfurt. So, playing in the Europa League is still not easy for Barcelona to win the title, but if Barcelona can win the title it is basically still better for them than nothing.
Because to win a title in the highest tournament like the Champions League is indeed difficult and not easy for every team to win it, so Barcelona should be able to understand this more and keep targeting to win another title this season.
I personally am not too confident that Xavi will still be appointed as Barcelona coach next season, if this season Barcelona doesn't win any titles then maybe Xavi will be fired.
Because Barcelona has made great efforts to bring in many luxury players with a difficult financial situation, but they are still difficult to win titles so the only way is to get a more appropriate coach.
I think it would be different this year, last year it was the first days of Xavi, he managed the team for a month or two before they had to play Frankfurt who eventually won the whole thing, which means it was difficult for them.
This year, it is still not guaranteed that they would win it, maybe United would eliminate them as well who knows, but this year Xavi has been managing the team for a total of nearly one year when they have to play United, that would mean that he would have the chance to establish his tiki taka back again, and that could result with a better result this time, because the strategy will be set. This isn't guaranteed of course, they might end up losing again, nobody knows.