Coaches can adapt themselves to our style and we can also adapt ourselves to their style. I'm sure that with a "defensive" coach , our team would learn how to defend and then we'd be more solid.
Tried that more than once. This season itself should show you it doesn't work. I think Lorenzo Serra Ferrer in 2001 was also sacked because of that.
Martino got the squad firing up pretty well in the beginning of the year, but the player that it benefited most was Fabregas, cause he plays better without possession and with a lot of space, while Iniesta wasn't at all comfortable playing that way, as can be seen in his performance then. Add to that the fact that we almost always won because of Valdes, and against 10 men in big games.
Barcelona have been playing possession based football for such a very, very long time and that it's become their identity. Take it away and you lose the essence of the team. As Xavi and Iniesta said, the style is really non-negotiable, but there needs to be coaches that can coach a team like Barca.
The idea with Tata was to try to add certain elements to the playing style, but what happened was that he completely changed the style, and when he had to play the way it suites them, unfortunately he couldn't do it well enough.