Barcelona having a great offensive line wouldn't be enough if they didn't had a great defensive line as well. Hansi Flick made some massive improvements on defense, he realized that the defensive line itself isn't good enough, and if they just parked the bus they would lose, so even in games where a tie is enough, they still play counter attacking at worst case, because they just prefer to make that a unison work that would allow them a chance.
Whatever it is that makes them so much better, it is not really what the yare after, what they want is to shadow the problems at defense until they get the title. After they do, and maybe open up some financials, they could get some defenders which could help the team immensely for the future.
If we look at what hansi flick is doing is actually quite reasonable in maintaining the balance of his team, often hansi flick emphasises every match with a big win and that is to anticipate that his team does not lose if the opposing team scores, so that way, they can secure every victory despite having a bad defence, the consistency shown by Barcelona is currently starting to improve and that further cements their position as the championship favourite, But even so, of course, Hansi Flick must begin to emphasize focus and better performance in the remaining matches with the tight schedule they currently have, if you look at their finances which are still very bad, of course the choice of bringing in new players next season is not a good choice, but the only way that Barcelona can do is to maximise the potential of young players and also existing players at this time.