Over the years, Barcelona have got us used to being dazzled by their brilliant performances. As you quite rightly said, the best defence is attack, but I often prefer to look at it differently: rather than thinking that attacking is the best defence, I believe that if you have possession of the ball, your opponents cannot hurt you and in that respect too, Barcelona have impressed us with their tiki-taka..
I think Barcelona's tiki-taka was once a clear winning trait, though after years it became just tiki-taka that didn't lead to anything. And this got boring because it slowed the game down significantly without creating any real dangerous situations. Flick's current style of play has brought this typical Spanish tiki-taka back to the heart of Barcelona's game, but with a bit more attacking flair that leads to goals.