Let's just remember some of the former transfers and high expectations:
Ferran = from high hopes to ridiculed by a majority in 6 Months
Griezz = 9 La liga goals in his first season, sold after 2 seasons
Frenkie De Jong = lost in space for 4 years. Came as the future best midfielder in the world
Arthur = 2nd best midfielder in the world. Ridiculed by a majority in the end
Dembele = 5 seasons of mysery. Injured and scored 3 goals in his 1st season
Coutinho = started ok, soon disappeared
Semedo = zero impact ever
Who was the last signing by Barca who had an immediate impact?
Also, who was the last signing from abroad who clicked well right away and made an impact?
Umtiti was the last one, iirc.
BBZ, I really like you because you are logical and analytical. The only difference between you and me is that you are a pessimist, and I am an optimist because football for me is a source of fun. We are both realists at heart mind you, even with all the other differences. If we were to talk about other subjects I would no doubt agree with you more, but football is not about being realistic, it's about being lighthearted and fun. It's not life and death, or anything even remotely close to that. It's about banter and jokes mostly.
You take it way too seriously, no offense.
I basically think you are generally right to be worried about these things. Most players will disappoint, no doubt. But some won't. The real fun about football is that, occasionally, you will discover special players that defy the odds and will be the real deal. Among Ardas, Arthurs and whatnot, you will discover awesome players and find underdog success stories.
And I believe the better the team running the club (manager, president, technical director), the better the odds of signing these players.
Let me tell you something, there is no doubt someone in 2003 (if Barcaforum would've been around at that time), would have made the same posts about Ronaldinho. The bottom line is that, generally, life is hard and the great stuff happens rarely. But not always, and some players are good enough to turn the table and defy statistics and probabilities.