Anyone who has been following La Liga for a long time will know that Barcelona is a club that has always rivaled Real Madrid for the La Liga title. I don't believe Barcelona was underestimated in La Liga last season; they only had a bad season in all competitions, which made them less competitive in all competitions last season. The tactics of Barcelona's new coach have helped Barcelona return to its winning ways and also make this La Liga season more competitive than last season. If Barcelona is consistent with their current form, Real Madrid will find it difficult to overtake Barcelona at the top of the La Liga table.
The major cause of Barcelona drop last season isn't stillclear to me though or let's just say they truly had a bad season just like you mentioned and remembered that the season Xavi joined the club they won the laliga but the following season which was last season I think turned out to be different. I don't know if same is going to repeat itself but I doubt it actually because I know Flick is more experienced and I could recall that the financial situation of Barca wasn't in a bad shape while Xavi took over but it's was in a critical state when Flick took over and still maintained it well, I guess that should explain alot...