Well, Xavi ranks amongst good coaches in europe today; but he does not rank as one of the most successful coaches in europe; and if Barcelona sack the dude today' they will face little difficulty replacing him.
The problem with Barcelona this season has to do with players depth, injury profiles and poor investment in the squad. No coach can fix such deficit.
Better for Barcelona board to trust the process with Xavi
The Barcelona board has given Xavi time to coach Barcelona and that is not only this season, but also the previous season. Now Barcelona also cannot completely blame the coach if there are still some shortcomings on the other side, such as in some of the aspects you said. Xavi might be able to be better at training Barcelona players, but if the players are still like they are now, it will also make Barcelona develop better because it is still not enough to make Barcelona strong again like before.