I am not trying to be argumentative for the sake of it. Again, you raise very good and fair points.
But, football fans are like the GF that always tells you that while you are great partner, you need to change X & Y in your personality, and keep insisting on it, until it makes the relationship about why you aren't changing for her. Instead of enjoining the good stuff.
Flick is who he is, he isn't going to make amendments of his coaching style. He always goes all in, he sticks to his beliefs to the core.
He has his shortcomings, and it is well pointed and documented. And the truth is, he isn't the best coach in the World, and there was a time when we were used to even better coaches.
But he is the best that we can get, that sticks to Barca number one principle: being entertaining.
He is stubborn, like plenty of great coaches, and there will come a time when we either have to make a significant changes in the team, or go in a different direction (likely more pragmatic) because as you say, it isn't sustainable.
The squad is good, probably between 4th to 7th best in the World, depending on who you ask. I think PSG, RM & Liverpool are safely better overall. Bayern & Arsenal are more complete but we have bigger difference makers, City I think is below us a bit though bigger depth again. We are ahead of the rest.
But we have the same ambitions of the top 3, which is a bit unrealistic. And he is fairly overachieving and allowing us to dream big for the most part.
Defense needs overhaul, we need at least one more difference maker in attack. We might need to sell in order to buy, but it is something we are allergic to.