Barcelona had a good season, you're right. Barcelona played well, beat and scored almost without fail, and only in the Europa League they were stopped by Manchester. We don't count the loss of the Champions League, it was more of a black streak for Barcelona.
That's why the failure after the championship looks so strange, considering the smooth and quality season.
If Real Madrid cannot reinforce with a top striker instead of Benzema and find replacements for Modric and Kroos, it's more likely that Barcelona will also become the champion next year.
I think the most important thing that the team needs right now is to make sure they get a better defense, the defense is the most important part they are lacking without a doubt. They are going to UCL again, this time as the head seed, I bet that they are going to face some inferior teams but I also believed they should have beaten Inter as well at the time, looking at it right now the team that beat them is at the finals so I wouldn't be really too shocked about it neither.
I guess they need to face some easier teams at first, and that might happen this time around. All in all they could get a greater defenders and if they could also get Messi as well, then they are ready, they need nothing else, all the rest of the team is ready to fight for a chance.