Barcelona is not strong in the Champions League, but Barcelona is the strongest team in La Liga, Copa Del Rey and Spanish Super Cup. Apart from lead the La Liga standings, Barcelona also has a good record from every home match where they only conceded 1 home goal in 9 matches. Barcelona is also the team with the best defense so far in La Liga where only 6 goals have been conceded in all league match.
Of course Real Sociedad are not a team to be underestimated, but this is a Copa Del Rey match that is likely to have different atmosphere for the two teams. Barcelona and Sociedad are fighting for semi-final ticket, and I believe Barcelona will win it.
The Copa Del Rey match organized by the Spanish federation is generally very different from La Liga, when Barcelona was able to compete with several clubs that contributed to the league, Barcelona was very good and finally Barcelona managed to win and advance to the semifinals. Barcelona's achievements are currently starting to recover and will be famous again.