Since Koeman arrival to Barcelona last season, Barcelona game has changed drastically, previously Barcelona continued to apply the tiki taka style, now that tiki taka style of play has begun to disappear since Koeman arrival, I think Barcelona current problem lies in tactics and style of play tend to stagnate so that their game is very easy for opponents to guess, and it can be seen when Barcelona are mercilessly crushed by Bayern Munich and even worse they seem to have difficulty winning when faced with a team that is below Barcelona level.
I agree with what you said, the impact of messi's departure has made Barcelona very depressed, just like what happened to Juventus after losing ronaldo this season.
Before, Barcelona used to play in Tiki-taka style. But now whether they play in any style or what their game plan is, I don't think they know it themselves. Even against a weaker team, I don't see a better performance from the Barcelona players. They also play defensively against weaker teams. Even against a weak team like Granda, Barcelona is not able to win now.
Don't stake too high on game's like Barcelona, probability of you getting things the wrong direction is high.
Tiki taka just as you have said ain't played recently..... I'm patiently waiting for the return of xavi Hernandez to Barcelona.
He'll sure put this into play,over there in Al sadd, carried the league with this style of play.
He should be the perfect one for this club, as well an overhaul will and should be done.